Using Quasars as a New Standard Candle to Define Distance

Quasar

A new study shows a way to use quasars to gauge distance in the early Universe.

The simple question of ‘how far?’ gets at the heart of the history of modern astronomy. Looking out across our galactic backyard into the primordial Universe, different yardsticks—often referred to as ‘standard candles’ —are used to gauge various distances, from near to far.

Continue reading “Using Quasars as a New Standard Candle to Define Distance”

A Galaxy is Making New Stars Faster Than its Black Hole Can Starve Them for Fuel

A monster lurks at the heart of many galaxies – even our own Milky Way. This monster possesses the mass of millions or billions of Suns. Immense gravity shrouds it within a dark cocoon of space and time – a supermassive black hole. But while hidden in darkness and difficult to observe, black holes can also shine brighter than an entire galaxy. When feeding, these sleeping monsters awaken transforming into a quasar – one of the Universe’s most luminous objects. The energy a quasar radiates into space is so powerful, it can interfere with star formation for thousands of light years across their host galaxies. But one galaxy appears to be winning a struggle against its awoken blazing monster and in a recent paper published in the Astrophysical Journal, astronomers are trying to determine how this galaxy survives.

Animation of Interstellar Matter Falling into a Black Hole Creating a Quasar – ESA
Continue reading “A Galaxy is Making New Stars Faster Than its Black Hole Can Starve Them for Fuel”

Supermassive black holes can cloak themselves in a cocoon of dust, making them invisible even when they should be bright quasars

Quasars are the most powerful sources of light in the universe, but sometimes they’re hard to find. A team of astronomers used the Chandra X-ray Space Telescope to find some diamonds in the rough.

Continue reading “Supermassive black holes can cloak themselves in a cocoon of dust, making them invisible even when they should be bright quasars”

For the First Time, Planets Have Been Discovered in ANOTHER Galaxy!

The first confirmed discovery of a planet beyond our Solar System (aka. an Extrasolar Planet) was a groundbreaking event. And while the initial discoveries were made using only ground-based observatories, and were therefore few and far between, the study of exoplanets has grown considerably with the deployment of space-based telescopes like the Kepler space telescope.

As of February 1st, 2018, 3,728 planets have been confirmed in 2,794 systems, with 622 systems having more than one planet. But now, thanks to a new study by a team of astrophysicists from the University of Oklahoma, the first planets beyond our galaxy have been discovered! Using a technique predicting by Einstein’s Theory of General Relativity, this team found evidence of planets in a galaxy roughly 3.8 billion light years away.

The study which details their discovery, titled “Probing Planets in Extragalactic Galaxies Using Quasar Microlensing“, recently appeared in The Astrophysical Journal Letters. The study was conducted by Xinyu Dai and Eduardo Guerras, a postdoctoral researcher and professor from the Homer L. Dodge Department of Physics and Astronomy at the University of Oklahoma, respectively.

For the sake of their study, the pair used the Gravitational Microlensing technique, which relies on the gravitational force of distant objects to bend and focus light coming from a star. As a planet passes in front of the star relative to the observer (i.e. makes a transit), the light dips measurably, which can then be used to determine the presence of a planet.

In this respect, Gravitational Microlensing is a scaled-down version of Gravitational Lensing, where an intervening object (like a galaxy cluster) is used to focus light coming from a galaxy or other large object located beyond it. It also incorporates a key element of the highly-effective Transit Method, where stars are monitored for dips in brightness to indicate the presence of an exoplanet.

In addition to this method, which is the only one capable of detecting extra-solar planets at truly great distances (on the order of billions of light years), the team also used data from NASA’s Chandra X-ray Observatory to study a distant quasar known as RX J1131–1231. Specifically, the team relied on the microlensing properties of the supermassive black hole (SMBH) located at the center of RX J1131–1231.

They also relied on the OU Supercomputing Center for Education and Research to calculate the microlensing models they employed. From this, they observed line energy shifts that could only be explained by the presence of of about 2000 unbound planets between the quasar’s stars – which ranged from being as massive as the Moon to Jupiter – per main-sequence star.

Image of the gravitational lens RX J1131-1231 galaxy with the lens galaxy at the center and four lensed background quasars. It is estimated that there are trillions of planets in the center elliptical galaxy in this image. Credit: University of Oklahoma

As Xinyu Dai explained in a recent University of Oklahoma press release:

“We are very excited about this discovery. This is the first time anyone has discovered planets outside our galaxy. These small planets are the best candidate for the signature we observed in this study using the microlensing technique. We analyzed the high frequency of the signature by modeling the data to determine the mass.”

While 53 planets have been discovered within the Milky Way galaxy using the Microlensing technique, this is the first time that planets have been observed in other galaxies. Much like the first confirmed discovery of an extra-solar planet, scientists were not even certain planets existed in other galaxies prior to this study. This discovery has therefore brought the study of planets beyond our Solar System to a whole new level!

And as Eduardo Guerras indicated, the discovery was possible thanks to improvements made in both modelling and instrumentation in recent years:

“This is an example of how powerful the techniques of analysis of extragalactic microlensing can be. This galaxy is located 3.8 billion light years away, and there is not the slightest chance of observing these planets directly, not even with the best telescope one can imagine in a science fiction scenario. However, we are able to study them, unveil their presence and even have an idea of their masses. This is very cool science.”

In the future, exoplanet discoveries are likely to be made within and beyond the Milky Way Galaxy. Credit: NASA

In the coming years, more sophisticated observatories will be available, which will allow for even more in the way of discoveries. These include space-based instruments like the James Webb Space Telescope (which is scheduled to launch in Spring of 2019) and ground-based observatories like the ESO’s OverWhelmingly Large (OWL) Telescope, the Very Large Telescope (VLT), the Extremely Large Telescope (ELT), and the Colossus Telescope.

At this juncture, the odds are good that some of these discoveries will be in neighboring galaxies. Perhaps then we can begin to determine just how common planets are in our Universe. At present, it is estimated that could be as many as 100 billion planets in the Milky Way Galaxy alone! But with an estimated 1 to 2 trillion galaxies in the Universe… well, you do the math!

Further Reading: University of Oklahoma, The Astrophysical Journal Letters

Too Big, Too Soon. Monster Black Hole Seen Shortly After the Big Bang

It is a well known fact among astronomers and cosmologists that the farther into the Universe you look, the further back in time you are seeing. And the closer astronomers are able to see to the Big Bang, which took place 13.8 billion years ago, the more interesting the discoveries tend to become. It is these finds that teach us the most about the earliest periods of the Universe and its subsequent evolution.

For instance, scientists using the Wide-field Infrared Survey Explorer (WISE) and the Magellan Telescopes recently observed the earliest Supermassive Black Hole (SMBH) to date. According to the discovery team’s study, this black hole is roughly 800 million times the mass of our Sun and is located more than 13 billion light years from Earth. This makes it the most distant, and youngest, SMBH observed to date.

The study, titled “An 800-million-solar-mass black hole in a significantly neutral Universe at a redshift of 7.5“, recently appeared in the journal Nature. Led by Eduardo Bañados, a researcher from the Carnegie Institution for Science, the team included members from NASA’s Jet Propulsion Laboratory, the Max Planck Institute for Astronomy, the Kavli Institute for Astronomy and Astrophysics, the Las Cumbres Observatory, and multiple universities.

Artist’s impression of ULAS J1120+0641, a very distant quasar powered by a black hole with a mass two billion times that of the Sun. Credit: ESO/M. Kornmesser

As with other SMBHs, this particular discovery (designated J1342+0928) is a quasar, a class of super bright objects that consist of a black hole accreting matter at the center of a massive galaxy. The object was discovered during the course of a survey for distant objects, which combined infrared data from the WISE mission with ground-based surveys. The team then followed up with data from the Carnegie Observatory’s Magellan telescopes in Chile.

As with all distant cosmological objects,  J1342+0928’s distance was determined by measuring its redshift. By measuring how much the wavelength of an object’s light is stretched by the expansion of the Universe before it reaches Earth, astronomers are able to determine how far it had to travel to get here. In this case, the quasar had a redshift of 7.54, which means that it took more than 13 billion years for its light to reach us.

As Xiaohui Fan of the University of Arizona’s Steward Observatory (and a co-author on the study) explained in a Carnegie press release:

“This great distance makes such objects extremely faint when viewed from Earth. Early quasars are also very rare on the sky. Only one quasar was known to exist at a redshift greater than seven before now, despite extensive searching.”

Given its age and mass, the discovery of this quasar was quite the surprise for the study team. As Daniel Stern, an astrophysicist at NASA’s Jet Propulsion Laboratory and a co-author on the study, indicated in a NASA press release, “This black hole grew far larger than we expected in only 690 million years after the Big Bang, which challenges our theories about how black holes form.”

This illustration shows the evolution of the Universe, from the Big Bang on the left, to modern times on the right. Image: NASA

Essentially, this quasar existed at a time when the Universe was just beginning to emerge from what cosmologists call the “Dark Ages”. During this period, which began roughly 380,000 years to 150 million years after the Big Bang, most of the photons in the Universe were interacting with electrons and protons. As a result, the radiation of this period is undetectable by our current instruments – hence the name.

The Universe remained in this state, without any luminous sources, until gravity condensed matter into the first stars and galaxies. This period is known as the “Reinozation Epoch”, which lasted from 150 million to 1 billion years after the Big Bang and was characterized by the first stars, galaxies and quasars forming. It is so-named because the energy released by these ancient galaxies caused the neutral hydrogen of the Universe to get excited and ionize.

Once the Universe became reionzed, photons could travel freely throughout space and the Universe officially became transparent to light. This is what makes the discovery of this quasar so interesting. As the team observed, much of the hydrogen surrounding it is neutral, which means it is not only the most distant quasar ever observed, but also the only example of a quasar that existed before the Universe became reionized.

In other words, J1342+0928 existed during a major transition period for the Universe, which happens to be one of the current frontiers of astrophysics. As if this wasn’t enough, the team was also confounded by the object’s mass. For a black hole to have become so massive during this early period of the Universe, there would have to be special conditions to allow for such rapid growth.

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).

What these conditions are, however, remains a mystery. Whatever the case may be, this newly-found SMBH appears to be consuming matter at the center of a galaxy at an astounding rate. And while its discovery has raised many questions, it is anticipated that the deployment of future  telescopes will reveal more about this quasar and its cosmological period. As Stern said:

“With several next-generation, even-more-sensitive facilities currently being built, we can expect many exciting discoveries in the very early universe in the coming years.”

These next-generation missions include the European Space Agency’s Euclid mission and NASA’s Wide-field Infrared Survey Telescope (WFIRST). Whereas Euclid will study objects located 10 billion years in the past in order to measure how dark energy influenced cosmic evolution, WFIRST will perform wide-field near-infrared surveys to measure the light coming from a billion galaxies.

Both missions are expected to reveal more objects like J1342+0928. At present, scientists predict that there are only 20 to 100 quasars as bright and as distant as J1342+0928 in the sky. As such, they were most pleased with this discovery, which is expected to provide us with fundamental information about the Universe when it was only 5% of its current age.

Further Reading: NASA, Carnegie Science, Nature

New Method for Researching Activity Around Quasars and Black Holes

Artist’s impression of ULAS J1120+0641, a very distant quasar powered by a black hole with a mass two billion times that of the Sun. Credit: ESO/M. Kornmesser

Ever since the discovery of Sagittarius A* at the center of our galaxy, astronomers have come to understand that most massive galaxies have a Supermassive Black Hole (SMBH) at their core. These are evidenced by the powerful electromagnetic emissions produced at the nuclei of these galaxies – which are known as “Active Galatic Nuclei” (AGN) – that are believed to be caused by gas and dust accreting onto the SMBH.

For decades, astronomers have been studying the light coming from AGNs to determine how large and massive their black holes are. This has been difficult, since this light is subject to the Doppler effect, which causes its spectral lines to broaden. But thanks to a new model developed by researchers from China and the US, astronomers may be able to study these Broad Line Regions (BLRs) and make more accurate estimates about the mass of black holes.

The study, “Tidally disrupted dusty clumps as the origin of broad emission lines in active galactic nuclei“, recently appeared in the scientific journal Nature. The study was led by Jian-Min Wang, a researcher from the Institute of High Energy Physics (IHEP) at the Chinese Academy of Sciences, with assistance from the University of Wyoming and the University of Nanjing.

An artist’s impression of the accretion disc around the supermassive black hole that powers an active galaxy. Credit: NASA/Dana Berry, SkyWorks Digital

To break it down, SMBHs are known for having a torus of gas and dust that surrounds them. The black hole’s gravity accelerates gas in this torus to velocities of thousands of kilometers per second, which causes it to heat up and emit radiation at different wavelengths. This energy eventually outshined the entire surrounding galaxy, which is what allows astronomers to determine the presence of an SMBH.

As Michael Brotherton, a UW professor in the Department of Physics and Astronomy and a co0author on the study, explained in a UW press release:

“People think, ‘It’s a black hole. Why is it so bright?’ A black hole is still dark. The discs reach such high temperatures that they put out radiation across the electromagnetic spectrum, which includes gamma rays, X-rays, UV, infrared and radio waves. The black hole and surrounding accreting gas the black hole is feeding on is fuel that turns on the quasar.”

The problem with observing these bright regions comes from the fact that the gases within them are moving so quickly in different directions. Whereas gas moving away (relative to us) is shifted towards the red end of the spectrum, gas that is moving towards us is shifted towards the blue end. This is what leads to a Broad Line Region, where the spectrum of the emitted light becomes more like a spiral, making accurate readings difficult to obtain.

Currently, the measurement of the mass of SMBHs in active galactic nuclei relies the “reverberation mapping technique”. In short, this involves using computer models to examine the symmetrical spectral lines of a BLR and measuring the time delays between them. These lines are believed to arise from gas that has been photoionized by the gravitational force of the SMBH.

Dense clouds of dust and gas, illustrated here, can obscure less energetic radiation from an active galaxy’s central black hole. High-energy X-rays, however, easily pass through. Credit: ESA/NASA/AVO/Paolo Padovani

However, since there is little understanding of broad emission lines and the different components of BLRs, this method gives rise to some uncertainties off between 200 and 300%. “We are trying to get at more detailed questions about spectral broad-line regions that help us diagnose the black hole mass,” said Brotherton. “People don’t know where these broad emission line regions come from or the nature of this gas.”

In contrast, the team led by Dr. Wang adopted a new type of computer model that considered the dynamics of the gas torus surrounding a SMBH. This torus, they assume, would be made up of discrete clumps of matter that would be tidally disrupted by the black hole, resulting in some gas flowing into it (aka. accreting on it) and some being ejected as outflow.

From this, they found that the emission lines in a BLR are subject to three characteristics – “asymmetry”, “shape” and “shift”. After examining various emissions lines – both symmetrical and asymmetrical – they found that these three characteristics were strongly dependent on how bright the gas clumps were, which they interpreted as being a result of the angle of their motion within the torus. Or as Dr. Brotherton put it:

“What we propose happens is these dusty clumps are moving. Some bang into each other and merge, and change velocity. Maybe they move into the quasar, where the black hole lives. Some of the clumps spin in from the broad-line region. Some get kicked out.”

Illustration of the supermassive black hole at the center of the Milky Way. Credit: NRAO/AUI/NSF
Illustration of the supermassive black hole at the center of the Milky Way.
Credit: NRAO/AUI/NSF

In the end, their new model suggests that tidally disrupted clumps of matter from a black hole torus may represent the source of the BLR gas. Compared to previous models, the one devised by Dr. Wang and his colleagues establishes a connection between different key processes and components in the vicinity of a SMBH. These include the feeding of the black hole, the source of photoionized gas, and the dusty torus itself.

While this research does not resolve all the mysteries surrounding AGNs, it is an important step towards obtaining accurate mass estimates of SMBHs based on their spectral lines. From these, astronomers could be able to more accurately determine what role these black holes played in the evolution of large galaxies.

The study was made possible thanks with support provided by the National Key Program for Science and Technology Research and Development, and the Key Research Program of Frontier Sciences, both of which are administered by the Chinese Academy of Sciences.

Further Reading: IHEP, UW News, Nature

Quasar Light Confirms Consistency Of Electromagnetism Over 8 Billion Years

Back in November, a team of researchers from the Swinburne University of Technology and the University of Cambridge published some very interesting findings about a galaxy located about 8 billion light years away. Using the La Silla Observatory’s Very Large Telescope (VLT), they examined the light coming from the supermassive black hole (SMBH) at its center.

In so doing, they were able to determine that the electromagnetic energy coming from this distant galaxy was the same as what we observe here in the Milky Way. This showed that a fundamental force of the Universe (electromagnetism) is constant over time. And on Monday, Dec. 4th, the ESO followed-up on this historic find by releasing the color spectrum readings of this distant galaxy – known as HE 0940-1050.

To recap, most large galaxies in the Universe have SMBHs at their center. These huge black holes are known for consuming the matter that orbits all around them, expelling tremendous amounts of radio, microwave, infrared, optical, ultra-violet (UV), X-ray and gamma ray energy in the process. Because of this, they are some of the brightest objects in the known Universe, and are visible even from billions of light years away.

 Artist’s interpretation of ULAS J1120+0641, a very distant quasar. Credit: ESO/M. Kornmesser

Artist’s interpretation of ULAS J1120+0641, a very distant quasar.
Credit: ESO/M. Kornmesser

But because of their distance, the energy which they emit has to pass through the intergalactic medium, where it comes into contact with incredible amount of matter. While most of this consists of hydrogen and helium, there are trace amounts of other elements as well. These absorb much of the light that travels between distant galaxies and us, and the absorption lines this creates can tell us of lot about the kinds of elements that are out there.

At the same time, studying the absorption lines produced by light passing through space can tell us how much light was removed from the original quasar spectrum. Using the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument aboard the VLT, the Swinburne and Cambridge team were able to do just that, thus sneaking a peak at the “fingerprints of the early Universe“.

What they found was that the energy coming from HE 0940-1050 was very similar to that observed in the Milky Way galaxy. Basically, they obtained proof that electromagnetic energy is consistent over time, something which was previously a mystery to scientists. As they state in their study, which was published in the Monthly Notices of the Royal Astronomical Society:

“The Standard Model of particle physics is incomplete because it cannot explain the values of fundamental constants, or predict their dependence on parameters such as time and space. Therefore, without a theory that is able to properly explain these numbers, their constancy can only be probed by measuring them in different places, times and conditions. Furthermore, many theories which attempt to unify gravity with the other three forces of nature invoke fundamental constants that are varying.

A laser beam launched from VLT´s 8.2-metre Yepun telescope crosses the majestic southern sky and creates an artificial star at 90 km altitude in the high Earth´s mesosphere. The Laser Guide Star (LGS) is part of the VLT´s Adaptive Optics system and it is used as reference to correct images from the blurring effect of the atmosphere. The picture field is crossed by an impressive Milky Way, our own galaxy seen perfectly edge-on. The most prominent objects on the Milky Way are: Sirius, the brightest star in the sky, visible at the top and the Carina nebula, seen as a bright patch besides the telescope. From the right edge of the picture to the left, the following objects are aligned: the Small Magellanic Cloud (with the globular cluster 47 Tucanae on its right), the Large Magellanic Cloud and Canopus, the second brightest star in the sky.
A laser beam launched from the Very Large Telescope (VLT) at the ESO’s La Silla Observatory in Chile. Credit: ESO

Since it is 8 billion light years away, and its strong intervening metal-absorption-line system, probing the electromagnetic spectrum being put out by HE 0940-1050 central quasar – not to mention the ability to correct for all the light that was absorbed by the intervening intergalactic medium – provided a unique opportunity to precisely measure how this fundamental force can vary over a very long period of time.

On top of that, the spectral information they obtained happened to be of the highest quality ever observed from a quasar. As they further indicated in their study:

“The largest systematic error in all (but one) previous similar measurements, including the large samples, was long-range distortions in the wavelength calibration. These would add a ?2 ppm systematic error to our measurement and up to ?10 ppm to other measurements using Mg and Fe transitions.”

However, the team corrected for this by comparing the UVES spectra to well-calibrated spectra obtained  from the High Accuracy Radial velocity Planet Searcher (HARPS) –  which is also located at the at the La Silla Observatory. By combining these readings, they were left with a residual systematic uncertainty of just 0.59 ppm, the lowest margin of error from any spectrographic survey to date.

High Accuracy Radial velocity Planet Searcher at the ESO La Silla 3.6m telescope. Credit: ESO
High Accuracy Radial velocity Planet Searcher at the ESO La Silla 3.6m telescope. Credit: ESO

This is exciting news, and for more reasons that one. On the one hand, precise measurements of distant galaxies allow us to test some of the most tricky aspects of our current cosmological models. On the other, determining that electromagnetism behaves in a consistent way over time is a major find, largely because it is responsible for such much of what goes on in our daily lives.

But perhaps most importantly of all, understanding how a fundamental force like electromagnetism behaves across time and space is intrinsic to finding out how it – as well as weak and strong nuclear force – unifies with gravity. This too has been a preoccupation of scientists, who are still at a loss when it comes to explaining how the laws governing particles interactions (i.e. quantum theory) unify with explanations of how gravity works (i.e general relativity).

By finding measurements of how these forces operate that are not varying could help in creating a working Grand Unifying Theory (GUT). One step closer to truly understanding how the Universe works!

Further Reading: ESO

How Cold Are Black Holes?

Today we’re going to have the most surreal conversation. I’m going to struggle to explain it, and you’re going to struggle to understand it. And only Stephen Hawking is going to really, truly, understand what’s actually going on.

But that’s fine, I’m sure he appreciates our feeble attempts to wrap our brains around this mind bending concept.

All right? Let’s get to it. Black holes again. But this time, we’re going to figure out their temperature.

The very idea that a black hole could have a temperature strains the imagination. I mean, how can something that absorbs all the matter and energy that falls into it have a temperature? When you feel the warmth of a toasty fireplace, you’re really feeling the infrared photons radiating from the fire and surrounding metal or stone.

And black holes absorb all the energy falling into them. There is absolutely no infrared radiation coming from a black hole. No gamma radiation, no radio waves. Nothing gets out.

As with most galaxies, a supermassive black hole lies at the heart of NGC 5548. Credit: ESA/Hubble and NASA. Acknowledgement: Davide de Martin

Now, supermassive black holes can shine with the energy of billions of stars, when they become quasars. When they’re actively feeding on stars and clouds of gas and dust. This material piles up into an accretion disk around the black hole with such density that it acts like the core of a star, undergoing nuclear fusion.

But that’s not the kind of temperature we’re talking about. We’re talking about the temperature of the black hole’s event horizon, when it’s not absorbing any material at all.

The temperature of black holes is connected to this whole concept of Hawking Radiation. The idea that over vast periods of time, black holes will generate virtual particles right at the edge of their event horizons. The most common kind of particles are photons, aka light, aka heat.

Normally these virtual particles are able to recombine and disappear in a puff of annihilation as quickly as they appear. But when a pair of these virtual particles appear right at the event horizon, one half of the pair drops into the black hole, while the other is free to escape into the Universe.

From your perspective as an outside observer, you see these particles escaping from the black hole. You see photons, and therefore, you can measure the temperature of the black hole.

PIA18919: How Black Hole Winds Blow (Artist's Concept)
Artist’s concept of the black hole at the center of the Pinwheel Galaxy. Credit: NASA/JPL-Caltech

The temperature of the black hole is inversely proportional to the mass of the black hole and the size of the event horizon. Think of it this way. Imagine the curved surface of a black hole’s event horizon. There are many paths that a photon could try to take to get away from the event horizon, and the vast majority of those are paths that take it back down into the black hole’s gravity well.

But for a few rare paths, when the photon is traveling perfectly perpendicular to the event horizon, then the photon has a chance to escape. The larger the event horizon, the less paths there are that a photon could take.

Since energy is being released into the Universe at the black hole’s event horizon, but energy can neither be created or destroyed, the black hole itself provides the mass that supplies the energy to release these photons.

The black hole evaporates.

The most massive black holes in the Universe, the supermassive black holes with millions of times the math of the Sun will have a temperature of 1.4 x 10^-14 Kelvin. That’s low. Almost absolute zero, but not quite.

Artist's impression of a feeding stellar-mass black hole. Credit: NASA, ESA, Martin Kornmesser (ESA/Hubble)
Artist’s impression of a feeding stellar-mass black hole. Credit: NASA, ESA, Martin Kornmesser (ESA/Hubble)

A solar mass black hole might have a temperature of only .0.00000006 Kelvin. We’re getting warmer.

Since these temperatures are much lower than the background temperature of the Universe – about 2.7 Kelvin, all the existing black holes will have an overall gain of mass. They’re absorbing energy from the Cosmic Background Radiation faster than they’re evaporating, and will for an incomprehensible amount of time into the future.

Until the background temperature of the Universe goes below the temperature of these black holes, they won’t even start evaporating.

A black hole with the mass of the Earth is still too cold.

Only a black hole with about the mass of the Moon is warm enough to be evaporating faster than it’s absorbing energy from the Universe.

As they get less massive, they get even hotter. A black hole with the mass of the asteroid Ceres would be 122 Kelvin. Still freezing, but getting warmer.

A black hole with half the mass of Vesta would blaze at more than 1,200 Kelvin. Now we’re cooking!

Less massive, higher temperatures.

When black holes have lost most of their mass, they release the final material in a tremendous blast of energy, which should be visible to our telescopes.

Artist's conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library
Artist’s conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library

Some astronomers are actively searching the night sky for blasts from black holes which were formed shortly after the Big Bang, when the Universe was hot and dense enough that black holes could just form.

It took them billions of years of evaporation to get to the point that they’re starting to explode now.

This is just conjecture, though, no explosions have ever been linked to primordial black holes so far.

It’s pretty crazy to think that an object that absorbs all energy that falls into it can also emit energy. Well, that’s the Universe for you. Thanks for helping us figure it out Dr. Hawking.

Will Our Black Hole Eat the Milky Way?

Want to hear something cool? There’s a black hole at the center of the Milky Way. And not just any black hole, it’s a supermassive black hole with more than 4.1 million times the mass of the Sun.

It’s right over there, in the direction of the Sagittarius constellation. Located just 26,000 light-years away. And as we speak, it’s in the process of tearing apart entire stars and star systems, occasionally consuming them, adding to its mass like a voracious shark.

Sagittarius A*. Image credit: Chandra
Sagittarius A*. Image credit: Chandra

Wait, that doesn’t sound cool, that sort of sounds a little scary. Right?

Don’t worry, you have absolutely nothing to worry about, unless you plan to live for quadrillions of years, which I do, thanks to my future robot body. I’m ready for my singularity, Dr. Kurzweil.

Is the supermassive black hole going to consume the Milky Way? If not, why not? If so, why so?

The discovery of a supermassive black hole at the heart of the Milky Way, and really almost all galaxies, is one of my favorite discoveries in the field of astronomy. It’s one of those insights that simultaneously answered some questions, and opened up even more.

Back in the 1970s, the astronomers Bruce Balick and Robert Brown realized that there was an intense source of radio emissions coming from the very center of the Milky Way, in the constellation Sagittarius.

They designated it Sgr A*. The asterisk stands for exciting. You think I’m joking, but I’m not. For once, I’m not joking.

An illustration of Saggitarius A*. Credit: NASA/CXC/M.Weiss

In 2002, astronomers observed that there were stars zipping past this object, like comets on elliptical paths going around the Sun. Imagine the mass of our Sun, and the tremendous power it would take to wrench a star like that around.

The only objects with that much density and gravity are black holes, but in this case, a black hole with millions of times the mass of our own Sun: a supermassive black hole.

With the discovery of the Milky Way’s supermassive black hole, astronomers found evidence that there are black holes at the heart of every galaxy.

At the same time, the discovery of supermassive black holes helped answer one of the big questions in astronomy: what are quasars? We did a whole article on them, but they’re intensely bright objects, generating enough light they can be seen billions of light-years away. Giving off more energy than the rest of their own galaxy combined.

The quasar SDSS J1106+1939 has the most energetic outflows ever seen, at least five times more powerful than any that have been observed to date. Credit: ESO/L. Calçada

It turns out that quasars and supermassive black holes are the same thing. Quasars are just black holes in the process of actively feeding; gobbling up so much material it piles up in an accretion disk around it. Once again, these do sound terrifying. But are we in any danger?

In the short term, no. The black hole at the center of the Milky Way is 26,000 light-years away. Even if it turned into a quasar and started eating stars, you wouldn’t even be able to notice it from this distance.

A black hole is just a concentration of mass in a very small region, which things orbit around. To give you an example, you could replace the Sun with a black hole with the exact same mass, and nothing would change. I mean, we’d all freeze because there wasn’t a Sun in the sky anymore, but the Earth would continue to orbit this black hole in exactly the same orbit, for billions of years.

Same goes with the black hole at the center of the Milky Way. It’s not pulling material in like a vacuum cleaner, it serves as a gravitational anchor for a group of stars to orbit around, for billions of years.

In order for a black hole to actually consume a star, it needs to make a direct hit. To get within the event horizon, which is only about 17 times bigger than the Sun. If a star gets close, without hitting, it’ll get torn apart, but still, it doesn’t happen very often.

A black hole, with an accretion disk, consuming a star. Credit: ESO/L. Calçada

The problem happens when these stars interact with one another through their own gravity, and mess with each other’s orbits. A star that would have been orbiting happily for billions of years might get deflected into a collision course with the black hole. But this happens very rarely.

Over the short term, that supermassive black hole is totally harmless. Especially from out here in the galactic suburbs.

But there are a few situations that might cause some problems over vast periods of time.

The first panic will happen when the Milky Way collides with Andromeda in about 4 billion years – let’s call this mess Milkdromeda. Suddenly, you’ll have two whole clouds of stars interacting in all kinds of ways, like an unstable blended family. Stars that would have been safe will careen past other stars and be deflected down into the maw of either of the two supermassive black holes on hand. Andromeda’s black hole could be 100 million times the mass of the Sun, so it’s a bigger target for stars with a death wish.

View of Milkdromeda from Earth "shortly" after the merger, around 3.85-3.9 billion years from now Credit: NASA, ESA, Z. Levay and R. van der Marel (STScI), T. Hallas, and A. Mellinger
View of Milkdromeda from Earth “shortly” after the merger, around 3.85-3.9 billion years from now Credit: NASA, ESA, Z. Levay and R. van der Marel (STScI), T. Hallas, and A. Mellinger

Over the coming billions, trillions and quadrillions of years, more and more galaxies will collide with Milkdromeda, bringing new supermassive black holes and more stars to the chaos.

So many opportunities for mayhem.

Of course, the Sun will die in about 5 billion years, so this future won’t be our problem. Well, fine, with my eternal robot body, it might still be my problem.

After our neighborhood is completely out of galaxies to consume, then there will just be countless eons of time for stars to interact for orbit after orbit. Some will get flung out of Milkdromeda, some will be hurled down into the black hole.

And others will be safe, assuming they can avoid this fate over the Googol years it’ll take for the supermassive black hole to finally evaporate. That’s a 1 followed by 100 zeroes years. That’s a really really long time, so now I don’t like those odds.

For our purposes, the black hole at the heart of the Milky Way is completely and totally safe. In the lifetime of the Sun, it won’t interact with us in any way, or consume more than a handful of stars.

But over the vast eons, it could be a different story. I hope we can be around to find out the answer.