Black Hole

Introduction

When looking up at the night sky, preferably on an unclouded night away from the corpulence of light pollution, one sees stars. With the unaided eye, one can perhaps see a few thousand stars dazzling in the night. That does not mean there are necessarily only a few thousand stars in the whole universe. In fact, the reader has an implicit knowledge that the number of stars in the universe must exceed this, whether from past learning or intuition combined with past learning. The number does exceed a few thousand for sure. With the aid of telescopes, below our atmosphere and above, a whole new world is literally illumined to us. For example, the Hubble space telescope in orbit of Earth has provided imagery for astronomers to garner that the number of stars is somewhere around 1023.1

Telescopes not only help us to see objects in the universe, like the aforementioned plethora of stars; but also help us to look farther back in time. Light, electromagnetic radiation, in its varying spectra, is received by our telescopes so that we are able to see objects far away and in the distant past. Electromagnetic radiation can only take us as far back as detectable however. For example, the cosmic microwave background is the “oldest” light in the universe, in which we detect the earliest stages of the universe. The classic image of the astronomer peering into a telescope stops here it seems. However, electromagnetic radiation is not the only tool offered to scientists studying the universe. Gravitational waves take us possibly further, ushering in a new age for physics and astronomy.

Gravitational Waves

Albert Einstein, one of the foremost physicists of the past century, formulated his General Theory of Relativity in 1915. From this theory, the existence of gravitational waves is mathematically derived.2 Einstein’s formulation of his breakthrough theory involved describing gravity as a geometric property of spacetime. Spacetime, geometrically speaking, is four dimensions: the three we ourselves move in (xyz) and the fourth included being time (the change we experience). Since gravity is so intimately connected with spacetime, one can understand gravitational waves simply as ripples or perturbations through spacetime. An object with mass, and hence a gravitational force attributed to it, will disturb spacetime and cause wavelike ripples. It can be analogously understood by your disturbance of water when you swim through a pool—the spacetime fabric, water in this case, is disturbed by an object with mass, your swimming, causing waves to emanate forth. These gravitational waves, caused by objects with mass, can also affect objects with mass, making them squeeze and stretch as waves pass through them—like a spring. Below is a figure depicting a mass distorting a 2D representation of spacetime.

3 Binary Pulsars Discovered

Einstein’s theory of General Relativity would take scientists on a 100 year long odyssey, from mathematical formulations, to the space age discovery of binary pulsars, and ultimately to the experimental detection of gravitational waves. Setting off to the space age, we see the discovery of a binary pulsar system. This turned out to be a major stride on the path to confirming the existenceof gravitational waves. “Taylor and Russell Hulse discovered in 1974 a binary system composed of a pulsar in orbit around a neutron star. Taylor and Joel M. Weisberg in 1982 found that the orbit of the pulsar was slowly shrinking over time because of the release of energy in the form of gravitational waves. For discovering the pulsar and showing that it would make possible this particular gravitational wave measurement, Hulse and Taylor were awarded the Nobel Prize in Physics in 1993.”

The two astronomers followed the mathematical derivations of gravitational waves, as laid out in General Relativity, and found their observations of the pulsars to be consistent with that of General Relativity’s proposals. To describe the concept: binary pulsars are high-density stars which orbit each other with high speed, and consequently, high energy. This high speed provides an emission of gravitational waves at a sufficiently high rate, where the two astronomers were able to observe over the course of many years that they were slowly getting closer to each other. This loss of energy and the amount lost is consistent with the mathematical formulations of Einstein’s Relativity. Below is the differential equation describing radial decay of a binary system.

dr dt = −64 5 G3 c5 (m1m2)(m1 + m2) r3

This differential equation describes the decay with time of a binary system collapsing on itself. This equation was used to describe the rate of decay of the binary pulsar system. The results were then compared to Einstein’s formulation of gravitational waves and their prescribed energy; to which the results coincided together almost perfectly. r is the distance between the two objects, t is the time, c is the speed of light, G is the gravitational constant. Solving the differential equation yields the time it takes for the binary to collapse in on itself.

t = 5 256 c5 G3 r4 (m1m2)(m1 + m2)

Detection

Detection of gravitational waves is no easy task. One can easily perceive visible light with their eyes, or use instrumentation to survey astronomical phenomena far away (cosmic microwave background). It is a whole other task to detect gravitational waves, mainly because their effects are so miniscule on the objects around us. However, as is seen with the binary pulsars described above, or with other similarly high-density/massive objects like black holes orbiting each other, gravitational waves are detectable with the instrumentation in use today. This leads us to the Laser Interferometer Gravitational-Wave Observatory (or LIGO), which successfully detected gravitational waves for the first time in 20154.

This instrument, far from a telescope, consists of two orthogonal long tubes, each four kilometers long, a laser interferometer at the origin, and two suspended mirrors. Since gravitational waves perturb spacetime, and subsequently objects which bend and stretch from this distortion, LIGO is the perfect instrument to detect sufficiently large gravitational waves. If any gravitational wave passes the detector, the arms of LIGO should stretch and the laser interferometers should detect that light was received at the origin of the detector and not cancelled out. If the light pulse sent through the two arms reflected back from the ends of the arms to the origin, the waves would cancel and thus gravitational waves would not be detected. But, the waves did not cancel in the historic moment of 2015, and instead the arms were indeed perturbed. Below is an excellent representation of LIGO5 provided by the LIGO team.

Conclusion

The century-long odyssey, from theory to detection, is an excellent feat of scientific triumph and human ingenuity. The significance of which heralds in a new frontier for physics. Just as the famous Star Trek opening goes, “Space, the final frontier. . . ”; we can similarly say, “Spacetime, the new frontier. . . ” Thats to say, gravitational wave astronomy/physics is a new and bustling field. It opens up new avenues of understanding the early universe, possibly even beyond what can be observed by mere electromagnetic waves.4

References

European Space Agency, Website URL https://www.esa.int/Our_Activities/Space_Science/Herschel/How_many_stars_are_there_in_the_Universe
Laser Interferometer Gravitational-Wave Observatory, Website URL,https://www.ligo.caltech.edu/page/what-are-gw, Operated by Caltech and MIT
Laser Interferometer Gravitational-Wave Observatory, Website URL,https://www.ligo.caltech.edu/news/ligo20160211, Operated by Caltech and MIT
Edwin F. Taylor and John Archibald Wheeler, Exploring Black Holes: An Introduction to General Relativity, Publisher: Addison Wesley Longman; 1 edition (July 22, 2000), Chapter 16
LIGO Multimedia Archives, https://www.ligo.org/multimedia.php

The question isn’t about whether dark matter exists or not. What’s going on is, when we measure gravity in the universe—the collective gravity of the stars, the planets, the moons, the gas clouds, the black holes, whole galaxies—when we do this, 85 percent has no known origin. So it’s not a matter of whether dark matter exists or not, it’s a measurement—period.

Now, “dark matter” is not even what we should be calling it because that implies that it is matter; it implies we know something about it that we actually don’t. So a more precise labeling for it would be “dark gravity.” Now, if I called it dark gravity, are you going to say: “Does dark gravity really exist?”

I’d say yeah, because 85 percent of the gravity has no known origin. There it is. Let’s figure out what’s causing it. The fact that the word “matter” got into that word is forcing people to say, “Well I have another idea, I bet it’s not matter, it could be something else!” We’re overreacting to a label that overstates our actual insights or knowledge into what it is we’re describing.

Then I just joke we should just call it Fred. Fred or Wilma, something where there is no reference to what we think it is because in fact we have no idea. So here’s how you actually measure the stuff. In a galaxy, which is the smallest aggregation of matter where dark matter manifests, you look how fast it’s rotating and we know from laws of gravity first laid down by Johannes Kepler and then enhanced and given further detail and deeper understanding by Isaac Newton, you write down these equations and say, look how fast it’s rotating, you invoke that rotation rate in the equation and out the other side says how much gravity, how much mass should be there attracting you.

And the more mass that’s there the faster we expect you to be orbiting. That kind of makes sense. So when you do this calculation on a galactic scale, we get vastly more mass attracting you than we actually can detect. I’m adding up stars, gas clouds, moon, planets, black holes—add it all up. It’s a fraction of what we know is attracting you in this orbit, and we cannot detect the rest and so we hand it this title dark matter.

Understandably, I suppose. But it implies that we know that it’s matter, but we don’t. We know we can’t detect it in any known way and we know it has gravity, so it really should be called dark gravity. I think the over–under on what dark matter might be, today, I think we’re all kind of leaning towards a family of particles, subatomic particles, that have hardly any ability to interact with the particles we have come to know and love, ‘ordinary matter’. And that would make it matter, dark matter, as we’ve all been describing it. And it’s not a weird thing that you could have a particle that doesn’t interact with our particles.

Within our own family of particles there are examples where the interaction is very weak or nonexistent. You might have heard of neutrinos, this is a ghost-like particle that permeates the universe and hardly interacts with familiar matter at all, yet it is part of our family of particles that we know exist and that we can detect and interact with. So if we can have an elusive particle that’s part of our own familiar family of particles it’s not much of a stretch to think of a whole other category of particles where none of them give a rat’s ass about the rest of us, and they just pass right through us as though we’re not even there.

Now, here’s what’s interesting about dark matter: we know it doesn’t interact with us except gravitationally. By the way, what do I mean by interact? Does it bind and make atoms and molecules and solid objects? No, it does not interact with us in any important known way. But it also doesn’t interact with itself. That’s what’s interesting. So if it interacted with itself you could imagine finding dark matter planets, dark matter galaxies, because to interact with yourself is what allows you to accumulate and have a concentration of matter in one place versus another. These are the atomic bonds and the molecular bonds that create solid objects.

And if particles do not interact with one another, they just pass through, you just have this zone of mass not really doing anything interesting. So dark matter not only doesn’t interact with us, it doesn’t interact with itself. And that’s why when we find dark matter across the universe it’s very diffusely spread out. It’s like over here. It’s not in this one spot and look at this concentration. No, that’s not how that works. An example of this: What is a rock? It’s a collection of atoms and molecules that are stuck together by electromagnetic forces. We don’t think of them that way, we just think of them as rocks, but they are held together by forces on the atomic and molecular scale, and they bind together and then we get what we call the solid object called a rock.

If those forces did not work on you as a particle, you have no occasion to bind with any other particle. You have no occasion—you have no ambitions of ever becoming a solid object. It’s a different kind of world, that would be. We would not expect that world to have life as we know it, because life requires an assembly of molecules to turn it into some separate entity distinct from everything else that then has fascinating chemical properties that we call life.

Conception

The idea of space-based observation had been floating around in the heads of many astronomers in the early 1900s. One of those astronomers was Lyman Spitzer, who wrote the paper Astronomical advantages of an extraterrestrial observatory. In this paper he envisioned telescope 500 miles above the earth, above atmospheric layers, equipped with various measuring devices for different phases of astronomic research. He anticipated that “Such a telescope could measure the spectra of stars, planets, etc. without the absorption of the earth’s atmosphere would have astronomical uses…obtaining information on the behavior of matter under conditions not in the laboratory, knowledge of fundamentals physics would thereby be enhanced”(1).

           Spitzer devoted his career to seeing a telescope to be put in space. While he served as the president of the American Astronomical Society and while working with the US space program in the 1960s, he led a program to design an earth orbiting observatory to study ultraviolet light. This project was a success, and was to be known as the Copernicus satellite. Soon Spitzers dream of launching a telescope into space would become a reality. Spitzer was able to convince Congress and the scientific community, the value of placing a telescope into space, giving birth to the very successful Orbiting Astronomical Observatory.

           The success of the Orbiting Astronomical Observatory was essential for the concept of the space telescope, and gave the confidence to the scientific community to pursue greater and more complex space telescope systems. Spitzer continued to lobby NASA and Congress to develop a space telescope. “In 1975, NASA, along with the European Space Agency, began development of what would become the Hubble Space Telescope” (2).

Journey into space

           The design and creation of the Hubble Space Telescope(HST) would be a collaboration between many institutions. Two of NASAs laboratories, the Marshal Space Flight Center(MSFC) and the Goddard Space Flight Center would be dividing the work. Marshal would be responsible for the design, development, and construction of the HST, while Goddard was responsible for the control of the scientific instruments and the ground control for the missions. Two other organizations were commissioned to work on the HST, Perkin-Elmer for the Optical Telescope Assembly and Guidance sensors, and Lockheed to construct the spacecraft in which all the components would be housed (3).

           In early 1986, close to the planned launch date of the Hubble, the program came to a halt. The Challenger accident had put to a stop to the US space program, causing the Hubble’s launch to be delayed several years(4). The telescope had to be stored until a new launch date could be scheduled. During this time, it did allow for Hubble’s engineers to double check all their work, swap out parts, run tests, and make other improvements to the telescope. In 1988, with the resuming of shuttle flights, the Hubble’s launch was schedule for April 24, 1990. The shuttle mission STS-21, flown by Discovery, successfully launched the Hubble Space Telescope into orbit (4).

Hubble Operation Setbacks

           Almost immediately after the launch of the Hubble, it was clear there was something very wrong. Hubble’s incredibly polished and accurate mirrors, could not focus properly. Hubble’s two and a half meter on eight point two foot mirror was rendered incapable by an error in its shapes less than one fiftieth of the width of a human hair. There was an aura of panic in the meetings and although there were actuators on the Hubble, designed to push and pull on the telescope mirror to fix small errors, this aberration was “seven times the dynamic range of the actuators”, meaning the problems is seven times larger than they can correct for (5). Discussions began on how to move forward with talk of using it in its current form, fixing it, or scrapping the project all together. Everyone involved with the Hubble was under fire, and the Hubble became known as a national disaster. Many solutions to the problem were possible, but almost all could not be completed while in space. After months of the Hubble floating in space, being completely unusable, a solution was formulated. Corrective lenses were to be placed in front of the sensor, essentially giving the Hubble glasses. The solution and repair, which I will discuss in more detail in a later section, was NASA’s greatest comeback story to date.

Getting data back to earth

           The raw data collected by the telescope have a long way to go before they become actual Hubble images. As Hubble completes a particular observation, it converts the starlight into digital signals. The digital signals are then relayed down to a ground station at White Sands, New Mexico through two orbiting Tracking and Data Relay Satellites. The ground station then relays the data to Goddard Space Flight Center’s ground control system, where staff ensure its completeness and accuracy. “Once the ground station transfers the data to Goddard, Goddard sends it to the Space Telescope Science Institute (STScI), where staff translate the data into scientifically meaningful units — such as wavelength or brightness — and archive the information on 5.25-inch magneto-optical disks”(6). The Hubble transmits a whopping 120 Gigabytes of data every week down to earth.

The use of the Hubble’s data and images by Astronomers around the world is very competitive and there is not enough time for every astronomer to get a turn. Astronomers must submit proposals in order to get access and control of the Hubble, and a review committee chooses what they deem to be the best proposals. “The winning proposals are the ones that make the best use of the telescope’s capabilities while addressing pressing astronomical questions. Each year around 1,000 proposals are reviewed and approximately 200 are selected, for a total of 20,000 individual observations”(6).

Servicing Missions and their Impact

Orbital servicing is the key to keeping Hubble in operating condition. “NASA’s orbital servicing plans address three primary maintenance scenarios: Incorporating technological advances into the science instruments, normal degradation of components , and random equipment failure or malfunction.”(7) Originally, planners considered using the Shuttle to return the telescope to Earth approximately every five years for maintenance. However, the idea was rejected for both technical and economic reasons. Returning Hubble to Earth would entail a significantly higher risk of contaminating or damaging delicate components. Ground servicing would require an expensive clean room and support facilities, including a large engineering staff, and the telescope would be out of action for a year or more—a long time to suspend scientific observations. Shuttle astronauts can accomplish most maintenance and refurbishment within an 11-day on-orbit mission with only a brief interruption to scientific operations and without the additional facilities and staff needed for ground servicing

Service Mission 1

           Because of the problem with the Hubble’s primary mirror, there was a lot of fear that Congress would write off the loss and move on. “The first servicing mission, already planned for 1993, then became much more than a simple scheduled service call: It became the only chance to save the program and the spacecraft from either euthanasia or perhaps resignation to living with its diminished performance” (4). The Optical Systems Failure Review board were grateful to find that the mirror was uniform in error. The team worked to find a ‘prescription’ for the aberrated mirror. When it was determined that the mirror was too flat by roughly 2 micrometers, or about 1/40th of a human hair, they were able to create a reverse prescription to correct the problem and a solution was now in the works. In the 1980s, a device was being constructed called the Space Telescope Axial Replacement(STAR), a potential replacement for one of the scientific instruments on the Hubble.

This device would be repurposed with corrective optics for the Hubble’s mirror, coining the name COSTAR. “COSTAR was a telephone booth-sized instrument which placed 5 pairs of corrective mirrors, some as small as a nickel coin, in front of the Faint Object Camera, the Faint Object Spectrograph and the Goddard High Resolution Spectrograph” (8).  The COSTAR was a complex system of mechanical components, mirrors, and electronics all controllable from earth. Since many of the scientific instruments depended on the Hubble’s primary mirror, the defection caused them to become obsolete, and special corrective changes needed to be made for each instrument to function as intended. In addition, the service mission included installation and replacement of various other parts of the Hubble, including an improved version of the Wide Field Planetary Camera, new solar arrays, sensors, and gyroscopes.

On January 13th, 1994 the mission was declared a success. At 11 days, 5 EVAs or Extra-Vehicular Activity periods, the first servicing mission was one of the most complicated and intensive missions performed of its time. ‘’It’s fixed beyond our wildest expectations,’ Program Scientist Ed Weiler beamed at a mid-January press conference. ‘The performance is as perfect as engineering can achieve and the laws of physics will allow(4).This successful mission not only improved Hubble’s vision — which led to a string of remarkable discoveries in a very short time — but it also validated the effectiveness of on-orbit servicing.

Service mission 2

After a successful first mission to correct Hubble’s vision in 1993, a second Servicing Mission (STS-82) was launched to the space telescope in February 1997. The goal of this 10-day operation was to enhance Hubble’s scientific capabilities for discovery by conducting a number of maintenance tasks and refurbishing the existing systems. There is no question that Hubble’s ‘first generation’ cameras gave us remarkable views of very distant galaxies. However, the light from the most distant galaxies is shifted to infrared wavelengths by the expanding universe. To see these galaxies, Hubble needed to be fitted with an instrument that could observe infrared light. STS-82 included the installation of two technologically advanced instruments by a crew of astronauts who reached Hubble aboard the Discovery Space Shuttle. Both devices featured technology that was not available when the first designs of the Hubble Space Telescope were produced. Provides Hubble with unique and powerful spectroscopic capabilities. A spectrograph separates the light gathered by the telescope into its spectral components so that the composition, temperature, motion, and other chemical and physical properties can be analyzed.

STIS’s two-dimensional detectors have allowed the instrument to gather 30 times more spectral data and 500 times more spatial data than the previous spectrographs on Hubble. These were capable of only looking at one place at a time. One of the greatest advantages to using STIS is in the study of supermassive black holes. STIS searches for massive black holes by studying the star and gas dynamics around galactic centers. It measures the distribution of matter in the universe by studying quasar absorption lines. It also uses its high sensitivity and spatial resolution to study star formation in distant galaxies and perform spectroscopic mapping of solar system objects.

The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) has let us gain valuable new information on the dusty centers of galaxies and the formation of stars and planets. NICMOS consists of three cameras. It is capable of both infrared imaging and spectroscopic observations of astronomical targets. NICMOS gave astronomers their first clear view of the universe at near-infrared wavelengths between 0.8 and 2.5 micrometers – longer wavelengths than the human eye can see. (The expansion of the universe shifts the light from very distant objects toward longer red and infrared wavelengths.)

NICMOS’s near infrared capabilities have provided views of objects too distant for research by previous Hubble optical and ultraviolet instruments. NICMOS’s detectors also perform more efficiently than previous infrared detectors. With its cryogenics depleted, NICMOS is now dormant and awaiting the installation of a new cooling system in SM3B.

Service Mission 3a and 3b

           Service mission 3, which took place in December of 1999, ended up being split into two missions. This was because three of the 6 gyroscopes had failed, parts that allow the Hubble to accurately point at specific locations. “Servicing Mission 3A successfully replaced equipment and performed maintenance upgrades to the Hubble Space Telescope. Although no new scientific instruments were installed, many activities took place over 3 EVA days” (10). Various components, including the Fine Guidance Sensor, which allows for stabilization during observation, thermal insulation blankets, and a more advanced computer system were installed during this mission.

           Service mission 3b, flown by the space shuttle Columbia in 2002, set out to upgrade the Hubble’s optics. The new instrument that was installed, the Advanced Camera for Surveys(ACS), would bring the decade old telescope into the 21st century. “ASC sees in wavelengths ranging from visible to far ultraviolet. It is actually a team of three different cameras with specialized capabilities” (11). This new camera doubled the Hubble’s field of view and allowed for 10 times the amount of data to be captured than its predecessor, the Wide Field and Planetary camera. Other components installed included new solar arrays, increasing power efficiency by 30 percent, and an update to the NICMOS, an infrared camera and spectrometer. These new additions to the Hubble allowed astronomers to conduct new, more efficient surveys of the universe.

Service mission 4

The Hubble Space Telescope was reborn with Servicing Mission 4 (SM4), the fifth and final servicing of the orbiting observatory. During SM4, two new scientific instruments were installed – the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3). Two failed instruments, the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys (ACS), were brought back to life by the first ever on-orbit repairs With these efforts, Hubble has been brought to the apex of its scientific capabilities. To prolong Hubble’s life, new batteries, new gyroscopes, a new science computer, a refurbished fine guidance sensor and new insulation on three electronics bays were also installed over the 12-day mission with five spacewalks. Additionally, a device was attached to the base of the telescope to facilitate de-orbiting when the telescope is eventually decommissioned.

Scientific discoveries

The Birth of the Universe

           One the biggest justification for building the Hubble Telescope was to determine the age of the universe. Before Hubble, the age of universe was estimated to be 10-20 billion years old, not a particular accurate guess. Hubble would be able to narrow down this estimate through the observation of Cepheid stars.” Cepheids are a special type of variable star with very stable and predictable brightness variations. The period of these variations depends on physical properties of the stars such as their mass and true brightness”(13). By observing Cepheids, astronomers can measure the changes of the stars intensity and dimness, which determines their ‘true brightness’. When comparing their ‘true brightness’ to their observed brightness, astronomers can then determine the distance to those stars and the galaxies they lay in.

           Because astronomers have Cepheid distances which can be accurately measured, they can now take those measurements over time to measure the distance they are moving away from us. “Hubble performed the definitive study of 31 Cepheid variable stars, helping to determine the current expansion rate and thereby narrow the age of the universe down to the most accurate it’s ever been…Its observations of Cepheid variable stars, combined with other measurements pinned down the age to 13.7 billion years old, plus or minus a few hundred million years”(14) By calculating the age of the universe, it gives us a timeline of how stars and galaxies are developed, and helped redefine how the universe and everything in it formed.

Hubble deep field

           One of Hubble’s most well-known accomplishments was an image created in 1995. This image, called the Hubble Deep Field, was created in a way not typical of the other Hubble images. The idea was to point the Hubble at nothing in particular, an area of sky where no observation had been made before. The point was to see how well the Hubble could observe distinct galaxies over long exposures with its various instruments. “The first Deep Field, the Hubble Deep Field North (HDF-N), was observed over 10 consecutive days during Christmas 1995. The resulting image[18] consisted of 342 separate exposures, with a total exposure time of more than 100 hours, compared with typical Hubble exposures of a few hours” (19). The results of this image were astonishing. “Almost 3000 galaxies were seen in the image. Scientists analyzed the image statistically and found that the HDF had seen back to the very young Universe where the bulk of the galaxies had not, as yet, had time to form stars” (19). By observing this small dark patch of sky, it revealed a world never seen before. It has inspired other subsequent observations of the sky in various other regions, revealing equally astonishing pictures. These images provided new glimpses of the early universe and generated a mass of scientific discoveries.

One of the most important changes brought on by the Deep Field images is how it changed the way astronomers share data. Instead of keeping the images and data to themselves, typical of scientific groups of the day, the team behind Deep Field immediately released their findings to the scientific community and to the public. This precedent was the starting point for changing the culture of astronomy, allowing for teams across the Astronomy community to be more open with their data and discoveries(19).

Black holes

Astronomers have found convincing evidence for a supermassive black hole in the center of our own Milky Way galaxy, the galaxy NGC 4258, the giant elliptical galaxy M87, and several others. Scientists verified the existence of the black holes by studying the speed of the clouds of gas orbiting those regions. In 1994, Hubble Space Telescope data measured the mass of an unseen object at the center of M87. Based on the motion of the material whirling about the center, the object is estimated to be about 3 billion times the mass of our Sun and appears to be concentrated into a space smaller than our solar system.

For many years, X-ray emissions from the double-star system Cygnus X-1 convinced many astronomers that the system contains a black hole. With more precise measurements available recently, the evidence for a black hole in Cygnus X-1 — and about a dozen other systems — is very strong.

Birth of stars        

           Observing the birth of stars has always been tricky, as they seem to take place in dusty environments, the view obstructed by ginormous clouds of gas “Dust clouds scatter visible light, but let infrared light through unimpeded, meaning infrared observations are often the only way to see young stars” (16). The Wide Field Camera 3 (WFC3) upgraded in service mission 4, is fitted with an infrared camera. This allows the Hubble to make both visible and infrared observations of the same location, as shown by the image.

           In the top half of the image, which was taken in visible light, shows the top of a “three-light-year-long pillar, bathed in the glow of light from hot, massive stars off the top of the image. Scorching radiation and fast winds from these stars are sculpting the pillar and causing new stars to form within it” (17).

           By contrast, the bottom image was taken with Hubble’s Infrared camera. The clouds of green and orange gas disappear almost completely, revealing the fledgling stars underneath. ‘’’This is the first time that we have actually seen the process of forming stars being uncovered by hotoevaporation,’ John Hester, lead designer on the WFC3 emphasized. ‘In some ways it seems more like archaeology than astronomy. The ultraviolet light from nearby stars does the digging for us, and we study what is unearthed’’’(17).

Future of the Hubble

The Hubble Space Telescope has been in orbit for over 28 years, 18 years over its planned 15 year lifep. Although there has been talk of a service mission extending the lifep of the Hubble into the 2020s, eventually the time of the Hubble will come to an end. Fortunately, there are telescopes being designed that will fulfil the legacy of the Hubble. One in particular, the James Webb Telescope, is designed to be the successor to the Hubble. The James Webb telescope is an improved version of the Hubble in almost every way. Its mirror will be twice the size of Hubble’s, allowing it “to detect objects 16 times fainter than Hubble” (18). Instead of orbiting around the earth the telescope will be placed in orbit at the Sun-Earth Lagrange point, allowing it to be orbiting the sun while shielded from its infrared light and heat by the earth. This, along with its specialized infrared telescope, will allow it to take the “clearest picture(s) ever of space objects that emit invisible radiation beyond the red end of the visible spectrum— early galaxies, infant stars, clouds of gas and dust, and much more” (19).

Abstract

This research paper will briefly introduce the reason behind the death of stars to set the foundation for supernovas, the concept of a supernova, and finally more specifically focus on what supernova remnants are. It will include research about their existence, how they behave, their classifications, what is known of them, and some recent findings about supernova remnants. Within these findings will be concepts such as the four stages a supernova goes through and the three variations in the types of supernova remnants that exist. Finally it will give a brief analysis of the M1 remnant that Charles Messier documented in his Messier Objects.

Death of a Star

Before delving deep into the phenomena that are supernova remnants, it is necessary to briefly explain matters such as how and why a star dies. Stars use up all of their “fuel.” This fuel is simply burning hydrogen. Whether or not a star will become a supernova depends on its mass (Gunn 2020). Therefore, lower mass stars will not be relevant to this paper as they do not become supernovas. High mass stars do.

Each star has two forces that act upon it pushing outward is the thermal gas that the star produces. Conversely, gravity tightly pulls inward towards the core of the star to give it its structure. These two forces act in a sort of tug-of-war until A star’s energy has run out. This is determined by how a star will burn certain elements of increasingly heavier density. A star cannot burn up to iron and will begin to destabilize at this point (Freudenrich 2020). The force of gravity wins the game of tug-of-war.

Supernovas

Without its fuel and the star’s core destabilized, it will begin to rapidly heat up and expand continuously. This process of shrinking and heating will continue until a star explodes as a supernova – the brightest explosion in the universe. Supernovas are so bright they can outshine entire galaxies for days or even months. A supernova occurs when a star is at least five times more dense than the sun (NASA 2019). Low mass stars do not turn into supernovas, hence why they are not relevant to this paper. When supernovas finish their explosion they will either turn into a neutron star of black hole depending on their mass.

What Are Supernova Remnants?

The aftermath of a supernova’s explosion will be supernova remnants. This is different from the star itself, which will take one of the two paths previously mentioned. The supernova remnants will burn as much energy as the sun has in three million years in just one day. (Mathis 2019).

Supernova remnants are important as they serve as a means of heating galaxies through their gas. This is done through their shocks and magnetism they produce after an explosion.

There are four main stages to a supernova remnant (Mathis 2019). The first stage is the initial explosion leading into a rapid expansion of the gas across the galaxy. This gas is millions of Kelvins hot and is only observable through X-rays. This first stage is capable of persisting for several centuries.

The second stage of supernova remnants begins when the temperature begins to cool as infinitesimal energy is sacrificed. For thousands of years this energy further expands at a lower temperature into the rest of the galaxy.

When the shell of the remnant acquires material that its mass is greater than or equal to itself, the third stage has been entered. This stage lasts for hundreds of thousands of years as it continues to radiate the beautifully colored energy and gas in the galaxy.

Finally, the fourth stage is reached when the remnants are no longer discernible as something unique and independent from the galaxy. It will reach pressure that is equal to that outside of its reach. Thus, concludes the life of supernova remnants.

There are three types of classification that supernova remnants fall under. The third category is an amalgamation of the first two and each is based on a specific property that is possesses. The first type are the shell-type remnants. These types of supernova remnants are characterized by how when they expand through their own galaxy they will heat up and energize things that they come into touch with. With this chain reaction unfolding, a sort of “shell” forms throughout the galaxy giving it its name. (Nasa n.d.)

A famous example of a shell type supernova remnant is the Cygnus Loop. It is estimated to have been created 5,000 years ago and has a distinct blue tinge to it. It is clearly a shell type remnant because “The filaments of gas and dust visible here in ultraviolet light were heated by the shockwave from the supernova, which is still spreading outward from the original explosion.” (NASA 2016).

The second type of supernova remnants are the crab-like remnants. They are denoted by their shape that can look like a ring. They emit various forms of energy like x-rays, the visible light spectrum, and even radio waves. The crab nebula is a famous example of this one, which has a purple hue to it.

Finally there are composite remnants which are simply a mixture of the shell and crab-like supernova remnants. They possess qualities of both.

The Crab Nebula of the Messier Marathon

Long ago in the eighteenth century lived a French astronomer by the name of Charles Messier. Messier would often stare into his telescope in the hopes of finding comets and other objects. When he stared into his telescope one night he discovered what he perceived to be a comet but in reality was simply a cluster of stars. He knew this as it was not moving. (Bakich 2020).

Messier began to publish a variety of things that he would refer to as nuisances when someone was searching for comets in the night sky. With all of his work documented, amateur and seasoned astronomers alike have come to use his 109 document “Messier Objects” of clusters, planets, and other astronomical objects to aid them in their own personal studies. By now the question has likely arisen as to why star clusters and French astronomers are worth noting in a term paper about supernova remnants. The answer is that the first of the 109 objects that Messier documented was in fact a supernova remnant – the Taurus M1 as it is known. In fact, it was the only supernova remnant that Messier noted on his list of nuisances in the sky.

Messier Number

NGC Number

Constellation

Type

Magnitude

M1

1952

Taurus

SNR

8

Above is an excerpt of the table found with the article detailing Messier’s findings. These details are worth some analysis about this constellation. The Messier Number for starts is simply its name. “M1.” It is derived from Messier’s last name starting with an M and that it was the first object he found in the night sky that he deemed worthy to be called a nuisance. There isn’t much to speak of there.

The NGC number is another form of classification. NGC stands for New General Catalogue. It was a system of classification created by a man named William Herschel after he and his sister pursued their ambitions of astronomy. It encompasses many different stars and objects in the sky. (Goldstein 2018). There is also not much to say of this without diverting from the topic of supernova remnants.

Skipping over the constellation classification of “Taurus” due to its obvious meaning that is it in the constellation of Taurus, its type of SNR will be explained next. SNR simply stands for “Supernova Remnant,” not to be confused with the “Signal-to-Noise” ratio that is used to measure magnitudes.

Following into magnitudes, the magnitude of this supernova remnant is 8. This means that the human eye alone cannot see this and it must be looked at through the use of a telescope. This system of classifying was derived from an ancient Greek by the name of Hipparchus of Nicea walking out one night and classifying stars into categories based upon how bright that they are (Mihos n.d.). The brightest stars were given the lowest numbers and the brightest the highest. Given that this star is beyond the scope of human sight, it is clear astronomers have had to state it is less luminous than a value of six. With further advanced telescopes, interpretation, and research, it is safe to assume that the crab-like remnant in the Taurus constellation has an apparent magnitude of eight.

Conclusion

This paper explored the factors that lead into a supernova remnant’s existence – the death of a star and a supernova’s explosion. Afterward it elaborated on the phases and types of supernova remnants that are present in our universe. Things like the crab-like remnants or the shell types to name two of them. Finally it was noted that the French astronomer of the name Charles Messier was lucky to number a supernova remnant in the Taurus constellation as the first of his Messier Objects. Deeper analysis was given based off of what Charles Messier’s M1 object’s properties were. Its classifications and it magnitude. Supernova remnants are both ephemeral and primordial in some cases. These phenomena are truly both beautiful and mysterious.

Works Cited

Administrator, NASA Content. “Cygnus Loop Nebula.” NASA, NASA, 26 May 2016, www.nasa.gov/mission_pages/galex/pia15415.html.
BAKICH, M. E. (2020). Run a Messier marathon. Astronomy, 48(3), 60–63.
Craig Freudenrich, Ph.D. “How Stars Work.” HowStuffWorks Science, HowStuffWorks, 27 Jan. 2020, science.howstuffworks.com/star6.htm.
Goldstein, Alan. “An NGC Primer.” Astronomy.com, 28 Aug. 2018, astronomy.com/magazine/2018/08/an-ngc-primer.
Gunn, Alastair. “How Do Stars Die?” BBC Science Focus Magazine, 2020, www.sciencefocus.com/space/how-do-stars-die/.
Mathis, John S. “Supernova Remnant.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 11 Mar. 2019, www.britannica.com/science/supernova-remnant.
Mihos, Chris. “The Magnitude Scale.” The Magnitude Scale, Case Western Reserve University, burro.case.edu/Academics/Astr221/Light/magscale.html.
“Supernova Remnants.” NASA, NASA, imagine.gsfc.nasa.gov/science/objects/supernova_remnants.html.
“What Is a Supernova?” NASA, NASA, 23 Oct. 2019, spaceplace.nasa.gov/supernova/en/.

Abstract

To fully understand what a nebula is and the useful function that they provide you must first understand the structure and build of the object. The research done in this essay takes you through all the steps starting with the foundational concept of the chemical makeup of what makes a nebula a nebula. Followed by process used to take useful data that would lay the foundation for the chemical structures of many nebula to follow. After words the next body takes you through the molecular cloud complex of the famous Orion nebula and gives you useful information about and how this single nebula is one of the most active solar nurseries, nearest to our own galaxy. The final body paragraph will explain and give the reader knowledge and insight to the Orion nebula after reading this last section you should have a vast take away of one of the most stunning Nebula available to you.

General Chemical Makeup of A Nebula

In order to understand how nebulas form, you must first understand the anatomy of what they are actually made out of. The first step to understanding the makeup of nebulas is to use a scientific device known as a spectrometer “An apparatus used for recording, and measuring spectrum, especially as a method of analysis” (“Spectrometer.” Dictionary.com, Dictionary.com, www.dictionary.com/browse/spectrometer.). Nebulas, being distant clouds of gas with no physical ground to land on, provides a challenge for scientist to collect important data on the composures of what makes a nebula a nebula; this is where the instrument of a spectrometer comes in handy. “The incident light from the light source can be transmitted, absorbed or reflected through the sample; The changes occurred during the interaction of incident light with the sample reveals the sample characteristics” (Walker, Kris. “Spectrometer Technology and Applications.” AZoM.com, AZoM.com, 1 Aug. 2017, www.azom.com/article.aspx?ArticleID=10245.). Spectrometer results of the Orion nebula reveal that the structure is composed of densely distributed material of mostly hydrogen, helium, and some plasma as well.

Depending on the type of nebula they all form in different ways, for instance when gravity begins to pull the hydrogen, helium, and stellar dust together and over a period of time the tightly packed material will generate a nebula. Another way nebula form is after a super nova. A supernova only occurs in two scenarios, the first being a degenerate star suddenly begin nuclear fusion once more. Usually the culprit that causes the first scenario to take place is a white dwarf collecting a satisfactory amount of energy from a binary companion to increase its core temperature causing a reaction known as runaway nuclear fusion causing devastation to the star. the second scenario is the collapse of the core of a massive star due to its energy output not being able to combat the force of gravity pushing back on the core of a star. As stated above when the core of a massive star can no longer resist the forces of gravity upon its core, the result is a sudden outburst of potential energy shooting from the core causing an explosion known as a super nova. The second scenario in a scientist aspect is a far more exciting and an explosive ending of a star’s life.

This reaction is very important to stellar formation as it replenishes the material needed for star formation into the interstellar median. The last way a nebula can form is from the transition of a red dwarf star to a white dwarf the end result of this process is either a black hole or neutron star are formed. When red dwarfs run out of hydrogen to fuse they either have enough nuclear energy depending on the size or not to combat the force of gravity causing the star to contract; when this happens the core begins to heat up beginning the process of helium fusion. When the process begins pressure starts to push causing the star to expand; the downfall of the star is now becoming more prominate as the temperature begins to decrease causing the star to glow redder and redder.

At this point a process known as helium flash starts to take place causing the helium stored inside the star to begin to fuse, the process takes anywhere from several. Minutes to a few hours but the definite time frame varies depending on several variables. As the star quickly starts fussing whatever elements are available to combat the gravitational collapse until there is nothing left to fuse within the star its self; depending on the size of the star determines its faith. If the remains are less then 1.4 solar masses of the sun it will become a white dwarf star, if it is greater than 1.4 solar masses of the sun than either the star will become a neutron star or a black hole even.

The Orion Nebula Cloud Complex

The Orion nebula is considered a star-forming region, a class of emission nebula know for giant molecular clouds. The Orion Molecular Cloud Complex is a star-forming region with two colossal molecular clouds designated Orion A and Orion B. Stars found within the complexes are still forming but there are many older stars not part of the complex any longer, one specific group of stars that comes to mind with this specific nebula would be the ones making up the silhouette of Orion’s belt. Scientist believe that the Orion Complex “is one of the most productive provinces of stellar formation noticeable in are local solar system; where both protoplanetary discs and very young stars can be found” (Gergesene, Erik. The Milky Way and beyond: Stars, Nebulae, and Other Galaxies. Britannica Educational Pub., 2010.). This Nebula is unique as well as the complex contains inside dark nebula, emission nebula, and reflective nebula as well.

Getting To Know The Orion Nebula

The Orion Nebula or Messier 42 is a diffuse nebula located south in the sword of the hunter Orion in the constellation of Orion with a visible magnitude of about + 4.0 nebula is 1,350 light years from earth and consist of hundreds of very young O-type stars at the heart of the nebula lies four massive stars known as the Trapezium. The Trapezium is very unique as it’s an open star cluster located in the heart of a nebula which results in most of the illumination around the nebula. According to NASA “Ultraviolent light unleashed by these stars is carving a cavity in the nebula and disrupting the growth of hundreds of smaller stars” (Garner, Rob. “Messier 42 (The Orion Nebula).” NASA, NASA, 6 Oct. 2017, www.nasa.gov/feature/goddard/2017/messier-42-the-orion-nebula). “It was discovered in 1618 by the French scholar Nicolas- Claude Fabri de Peiresc and independently in 1618 by the Swiss astronomer Johann Cyst” (Gergesene, Erik.

The Milky Way and beyond: Stars, Nebulae, and Other Galaxies. Britannica Educational Pub., 2010.), Furthermore in 1880 it was the first nebula to ever be photographed by Henry Draper. With advances in technology in the 1980s scientist were able to take the inferred spectroscopy of the Orion nebula and made several discoveries; the most important being a jet related to the birth of young stars. It is believed by scientist that these rich areas of gas, dust, and other material aids as a nursery so to speak for star formation; later in the process, the remaining material will eventually lead to planetary birth as well. There is evidence already pointing to early planetary formation as astronomers are already seeing young stars with debree disk already around them. visible to the naked eye the Orion Nebula is often a first deep space object for amateurs, but don’t be fooled it is also a site for professional astronomers as well. With the aid of 10 by 50 binoculars or a small telescope, the viewer is rewarded with great detail of the swirling gas and glistening stars in this nebula.

Other Nebula types

Vastly different from the Orion nebula is M1 or the Crab Nebula, located in the arm of Perseus with an apparent magnitude of just over +8.4. The reason I chose to use this nebula as topic on this paper was to show the importance of this nebula as it was the first recorded supernova remnant associated with an explosion.

Conclusion

Clearly, after reading this paper, you should know about the different categories of nebula discovered in are vastly infinite solar system; as well as the vastly different ways these beautiful objects come to fruition. Furthermore, you should also have a new prospective not only about the Orion nebula but many more nebulas out there like this one. I hope that you enjoyed this paper as much as I did writing it as I feel knowledge to new concepts is not only a very satisfying takeaway in my eyes, but opening other eyes as well is more important as well. So, I leave you with this final note I hope after reading this paper you can tell someone else about the formation of nebulas, molecular clouds, the locations at which stars are born, and finally new facts about the Orion nebula you can pass on to other so they can enjoy it just as much as I did.

The start of a black hole’s life comes from the end of a very large star’s life. A black hole occurs after a supernova explosion. That star usually has a very big core. A star the size of our sun will end its life as a black dwarf, a medium-sized star will end its life as a neutron star, and a star many times the size of our sun will form into black hole. ( https://study.com/academy/lesson/black-holes-and-neutron-star-life-cycle.html )

Explanation: black hole

A black hole is a place or region of space where the gravity force is so strong that no matter can get out once inside, not even light. Since no light can get out of a black hole, it is invisible. Scientists use special telescopes and tools to spot black holes. Those special tools are also used to see how stars that are closer to black holes act differently than normal stars that are further away from black holes. A black hole is not just empty space. It is anything but that. A black hole is an area with a very large amount of matter packed into a small space. Black holes are so dense that they make ‘gravity sinks’.

Description: black hole

A black hole is a massive thing in space that is invisible to the human eye. A black hole cannot be seen because the gravity pull is so strong that it is pulling the light into the holes’ centre. A black hole is not black, as you would expect. It just appears black because no light can get out of it. ( https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-black-hole-58.html )

Do Black Holes exist?

Yes, black holes exist! We have proof. Astronomers found evidence of a black hole that is massive in the centre of the milky way. Scientists had researched by studying a clouds speed orbiting around that specific region. There have also been many other black holes in the galaxy NGC 4258 etc. ( http://hubblesite.org/reference_desk/faq/answer.php.id=64&cat=exotic )

Event Horizon

An event horizon is the boundary defining the region of space around a black hole. It’s basically where one thing goes in, and it doesn’t come out again ( https://www.britannica.com/topic/event-horizon-black-hole ). The event horizon is the boundary marking the limits of a black hole, where nothing can escape once it goes in because nothing can travel faster than the speed of light, and as it states, nothing, not even light can escape a black hole. Which means it has to be faster than light to escape, physically nothing has been proven to be faster than the speed of light. ( https://www.quora.com/What-is-an-event-horizon-of-a-black-hole )

Why do scientists study black holes?

Scientists study black holes because they say it is connected to understanding gravity. Scientists say that it will help blind people have a better standard of living. ( http://curious.astro.cornell.edu/about-us/86-the-universe/black-holes-and-quasars/general-questions/440-why-do-we-study-black-holes-beginner )

Conclusion

In conclusion a black hole is a region in space that starts from a very large exploded star, where once something is in, it cannot get out. A black hole is invisible to the human eye because no light can get out of it.

Black holes are volumes of space where gravity is extreme to prevent the escape of even the fastest moving particles. The gravity is so strong because the matter has been compressed into tiny space. This can be formed by the death of massive star. They are invisible because there is no light and people cannot see the black hole’s.

Galaxy M87

The Galaxy M87, also known as Virgo A or NGC H487 is a supergiant elliptical galaxy. It is one of the brightest radio sources among the thousands of galactic systems in the sky. It is also a powerful X-ray source which suggests the presence of very hot gas in the galaxy.

Einsteins’s Theory

By general theory of relativity Albert Einstein proposed the existence of black holes. It has been known for decades. To prove the presence of black hole, the stars are being rotated around the invisible object in the centre of the Milky Way Galaxy.

Evidence of The Black Hole

The first ever direct visual evidence of a black hole in the centre of the galaxy M87 was released on April 10, 2019.it is located 55 million light years from earth. A team of more than 200 astrophysicists worked hard together to capture the image but the black hole image was not shown because it was black so it was invisible against the backdrop of the space. The scientists used radio signals to capture the black hole’s shadow.

Due to the gravitational force from the black hole, the light bends around the hole as a boundary and hence a bright ring is formed around the boundary of the black hole. The Event Horizontal Telescope project director Sheperd Doeleman told the reporters at the press conference in Washington DC that the evidence for a black hole is known now.

With Einstein’s prediction the evidence and the shape of the shadow is consistent. The black hole spins fast enough and they form a wormhole in spacetime. The M87 black hole is about 6.5 billion times the mass of the sun captured using the Event Horizon Telescope.

Operation Behind The First Ever Image of Black Hole

Combining a network of eight powerful ground based telescope a radio array was formed as wide as the earth. The observatories, located in Hawaii, Arizona, Chile, Mexico, Spain and Antarctica. The black hole’s radio were capture individually over four nights in April 2017 when the weather was optimal in all the six regions. Each telescope acquired the data from the target black hole.

Physical hard drives were used to store the data. It is then transported to the central location. It was stitched together by a super computer to form the image of the black hole’s shadow. Due to its enormous mass and relative time to earth, the researches who targeted the M87’s black hole say that the image produced is slightly blurry.

They say that the future image will be more clear because more telescopes are added to the Event Horizon Telescope. Sheperd Doeleman said that the collaboration is still working on producing an image of the Milky Way’s black hole and hoping to get that very soon. The team also believes that they will be able to fine-tune the photo further.

Further Achievements

The Event Horizon Telescope has also been trying to image the black hole closer. They had two primary targets. First was the Sagittarius A* which occupies 25,000 light year away from the earth at the centre of the Milky Way galaxy. It has a mass of about 4m suns. It is small enough that appears about the same size in the sky as much further M87. The second target was a supermassive black hole in the galaxy M87 into which the light and matter has disappeared.

The data collected by the telescope are currently in process by the scientists. The black holes are regions in space where the pulling strength of gravity is so powerful that even lights is unable to escape. Size and mass of the black hole can vary widely. The intense gravity is caused by the matter that is compressed into a small space. The black hole light is brightest among all the stars in the galaxy due to the far distance from the earth. Researches believe that the massive black holes which exist in the centre of the every galaxy in the universe were formed at the same time as their galaxy.

Conclusion

As the result the structure of black hole is nearly circular, as per the prediction of Einstein. It states that the observed image is consistent with expectations for the shadow of the spinning Kerr black hole as predicted by general relativity.