Even the Quiet Supermassive Black Holes are Blasting out Neutrinos and Gamma Rays

Is there anywhere in the Universe where we can escape from radiation? Certainly not here on Earth. And not in space itself, which is filled with diffuse radiation in the form of gamma rays and neutrinos. Scientists have struggled to explain where all those gamma rays and neutrinos come from. A trio of researchers is proposing a source for all that radiation in a new paper: resting black holes.

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This is How a Supermassive Black Hole Feeds

At the heart of most massive galaxies in our Universe, there are supermassive black holes (SMBH) on the order of millions to billions of times the mass of the Sun. As these behemoths consume gas and dust that’s slowly fed into their maws, they release tremendous amounts of energy. This leads to what is known as an Active Galactic Nucleus (AGN) – aka. a quasar – which can sometimes send hypervelocity jets of material for light-years.

Since they were first discovered, astrophysicists have suspected that SMBHs play an important role in the formation and evolution of galaxies. However, as a result, there has also been considerable research dedicated to how these massive objects form and evolve themselves. Recently, a team of astrophysicists conducted a high-powered simulation that showed exactly how SMBHs feed and determined that a galaxy’s arms play a vital role.

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The Event Horizon Telescope Zooms in on Another Supermassive Black Hole

On April 10th, 2019, the world was treated to the first image of a black hole, courtesy of the Event Horizon Telescope (EHT). Specifically, the image was of the Supermassive Black Hole (SMBH) at the center of the supergiant elliptical galaxy known as M87 (aka. Virgo A). These powerful forces of nature are found at the centers of most massive galaxies, which include the Milky Way (where the SMBH known as Sagittarius A* is located).

Using a technique known as Very-Long-Baseline Interferometry (VLBI), this image signaled the birth of a new era for astronomers, where they can finally conduct detailed studies of these powerful forces of nature. Thanks to research performed by the EHT Collaboration team during a six-hour observation period in 2017, astronomers are now being treated to images of the core region of Centaurus A and the radio jet emanating from it.

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When Galaxies Collide, Black Holes Don’t Always Get the Feast They Were Hoping for

What happens when galaxies collide? Well, if any humans are around in about a billion years, they might find out. That’s when our Milky Way galaxy is scheduled to collide with our neighbour the Andromeda galaxy. That event will be an epic, titanic, collision. The supermassive black holes at the center of both galaxies will feast on new material and flare brightly as the collision brings more gas and dust within reach of their overwhelming gravitational pull. Where massive giant stars collide with each other, lighting up the skies and spraying deadly radiation everywhere. Right?

Maybe not. In fact, there might be no feasting at all, and hardly anything titanic about it.

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Supermassive Black Hole Orbits an Even More Massive Black Hole, Crashing Through its Accretion Disk Every 12 Years

NASA’s Spitzer Space Telescope may be retired, but the things it witnessed during its sixteen and a half year mission will be the subject of study for many years to come. For instance, Spitzer is the only telescope to witness something truly astounding occurring at the center of the distant galaxy OJ 287: a supermassive black hole (SMBH) orbited by another black hole that regularly passes through its accretion disk.

Whenever this happens, it causes a flash that is brighter than all the stars in the Milky Way combined. Using Spitzer‘s observations, an international team of astronomers was able to finally create a model that accurately predicts the timing of these flashes and the orbit of the smaller black hole. In addition to demonstrating General Relativity in action, their findings also provide validation to Stephen Hawking‘s “no-hair theorem.”

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Some Quasars Shine With the Light of Over a Trillion Stars

Quasars are some of the brightest objects in the Universe. The brightest ones are so luminous they outshine a trillion stars. But why? And what does their brightness tell us about the galaxies that host them?

To try to answer that question, a group of astronomers took another look at 28 of the brightest and nearest quasars. But to understand their work, we have to back track a little, starting with supermassive black holes.

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New Technique for Estimating the Mass of a Black Hole

Black holes are the one the most intriguing and awe-inspiring forces of nature. They are also one of the most mysterious because of the way the rules of conventional physics break down in their presence. Despite decades of research and observations there is still much we don’t know about them. In fact, until recently, astronomers had never seen an image of black hole and were unable to guage their mass.

However, a team of physicist from the Moscow Institute of Physics and Technology (MIPT) recently announced that they had devised a way to indirectly measure the mass of a black hole while also confirming its existence. In a recent study, they showed how they tested this method on the recently-imaged supermassive black hole at the center of the Messier 87 active galaxy.

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Astronomers Find a Supermassive Black Hole That’s Feasting on a Regular Schedule, Every 9 Hours

Astronomers have found a supermassive black hole (SMBH) with an unusually regular feeding schedule. The behemoth is an active galactic nucleus (AGN) at the heart of the Seyfert 2 galaxy GSN 069. The AGN is about 250 million light years from Earth, and contains about 400,000 times the mass of the Sun.

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The Universe’s Missing Matter. Found!

In the 1960s, astronomers began to notice that the Universe appeared to be missing some mass. Between ongoing observations of the cosmos and the the Theory of General Relativity, they determined that a great deal of the mass in the Universe had to be invisible. But even after the inclusion of this “dark matter”, astronomers could still only account for about two-thirds of all the visible (aka. baryonic) matter.

This gave rise to what astrophysicists dubbed the “missing baryon problem”. But at long last, scientists have found what may very well be the last missing normal matter in the Universe. According to a recent study by a team of international scientists, this missing matter consists of filaments of highly-ionized oxygen gas that lies in the space between galaxies.

The study, titled “Observations of the missing baryons in the warm–hot intergalactic medium“, recently appeared in the scientific journal Nature. The study was led by Fabrizio Nicastro, a researcher from the Istituto Nazionale di Astrofisica (INAF) in Rome, and included members from the SRON Netherlands Institute for Space Research, the Harvard–Smithsonian Center for Astrophysics (CfA), the Instituto de Astronomia Universidad Nacional Autonoma de Mexico, the Instituto Nacional de Astrofísica, Óptica y Electrónica, the Instituto de Astrofísica de La Plata (IALP-UNLP) 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

For the sake of their study, the team consulted data from a series of instruments to examine the space near a quasar called 1ES 1553. Quasars are extremely massive galaxies with Active Galactic Nuclei (AGN) that emit tremendous amounts of energy. This energy is the result of gas and dust being accreted onto supermassive black holes (SMBHs) at the center of their galaxies, which results in the black holes emitting radiation and jets of superheated particles.

In the past, researchers believed that of the normal matter in the Universe, roughly 10% was bound up in galaxies while 60% existed in diffuse clouds of gas that fill the vast spaces between galaxies. However, this still left 30% of normal matter unaccounted for. This study, which was the culmination of a 20-year search, sought to determine if the last baryons could also be found in intergalactic space.

This theory was suggested by Charles Danforth, a research associate at CU Boulder and a co-author on this study, in a 2012 paper that appeared in The Astrophysical Journal – titled “The Baryon Census in a Multiphase Intergalactic Medium: 30% of the Baryons May Still be Missing“. In it, Danforth suggested that the missing baryons were likely to be found in the warm-hot intergalactic medium (WHIM), a web-like pattern in space that exists between galaxies.

As Michael Shull – a professor of Astrophysical and Planetary Sciences at the University of Colorado Boulder and one of the co-authors on the study – indicated, this wild terrain seemed like the perfect place to look.“This is where nature has become very perverse,” he said. “This intergalactic medium contains filaments of gas at temperatures from a few thousand degrees to a few million degrees.”

Close-up of star near a supermassive black hole (artist’s impression). Credit: ESA/Hubble, ESO, M. Kornmesser

To test this theory, the team used data from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to examine the WHIM near the quasar 1ES 1553. They then used the European Space Agency’s (ESA) X-ray Multi-Mirror Mission (XMM-Newton) to look closer for signs of the baryons, which appeared in the form of highly-ionized jets of oxygen gas heated to temperatures of about 1 million °C (1.8 million °F).

First, the researchers used the COS on the Hubble Space Telescope to get an idea of where they might find the missing baryons in the WHIM. Next, they homed in on those baryons using the XMM-Newton satellite. At the densities they recorded, the team concluded that when extrapolated to the entire Universe, this super-ionized oxygen gas could account for the last 30% of ordinary matter.

As Prof. Shull indicated, these results not only solve the mystery of the missing baryons but could also shed light on how the Universe began. “This is one of the key pillars of testing the Big Bang theory: figuring out the baryon census of hydrogen and helium and everything else in the periodic table,” he said.

Looking ahead, Shull indicated that the researchers hope to confirm their findings by studying more bright quasars. Shull and Danforth will also explore how the oxygen gas got to these regions of intergalactic space, though they suspect that it was blown there over the course of billions of years from galaxies and quasars. In the meantime, however, how the “missing matter” became part of the WHIM remains an open question. As Danforth asked:

“How does it get from the stars and the galaxies all the way out here into intergalactic space?. There’s some sort of ecology going on between the two regions, and the details of that are poorly understood.”

Assuming these results are correct, scientists can now move forward with models of cosmology where all the necessary “normal matter” is accounted for, which will put us a step closer to understanding how the Universe formed and evolved. Now if we could just find that elusive dark matter and dark energy, we’d have a complete picture of the Universe! Ah well, one mystery at a time…

Further Reading: UCB, Nature

Researchers Tackle Question of How the Universe Became Filled With Light

In accordance with the Big Bang model of cosmology, shortly after the Universe came into being there was a period known as the “Dark Ages”. This occurred between 380,000 and 150 million years after the Big Bang, where 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.

Astrophysicists and cosmologists have therefore been pondering how the Universe could go from being in this dark, cloudy state to one where it was filled with light. According to a new study by a team of researchers from the University of Iowa and the Harvard-Smithsonian Center for Astrophysics, it may be that black holes violently ejected matter from the early Universe, thus allowing light to escape.

Their study, titled “Resolving the X-ray emission from the Lyman continuum emitting galaxy Tol 1247-232“, recently appeared in the Monthly Notices of the Royal Astronomical Society. Led by Phillip Kaaret, a professor of Physics and Astronomy at the University of Iowa – and supported by an award from the Chandra X-ray Observatory – the research team arrived at this conclusion by observing a nearby galaxy from which ultraviolet light is escaping.

Milestones in the history of the Universe, from the Big Bang to the present day. Credit: NAOJ/NOAO

This galaxy, known as Tol 1247-232, is a small (and possibly elliptical) galaxy located 652 million light-years away, in the direction of the southern Hydra constellation. This galaxy is one of just nine in the local Universe (and one of only three galaxies close to the Milky Way) that has been shown to emit Lyman continuum photons – a type of radiation in the ultraviolet band.

Back in May of 2016, the team spotted a single X-ray source coming from a star-forming region in this galaxy, using the Chandra X-ray observatory. Based on their observations, they determined that it was not caused by the formation of a new star. For one, new stars do not experience sudden changes in brightness, as this x-ray source did. In addition, the radiation emitted by new stars does not come in the form of a point-like source.

Instead, they determined that what they were seeing had to be the result of a very small object, which left only one likely explanation: a black hole. As Philip Kaaret, a professor in the UI Department of Physics and Astronomy and the lead author on the study, explained:

“The observations show the presence of very bright X-ray sources that are likely accreting black holes. It’s possible the black hole is creating winds that help the ionizing radiation from the stars escape. Thus, black holes may have helped make the universe transparent.”

Where is the Nearest Black Hole
Artist concept of matter swirling around a black hole. Credit: NASA/Dana Berry/SkyWorks Digital

However, this also raised the question of how a black hole could be emitting matter. This is something that astrophysicists have puzzled over for quite some time. Whereas all black holes have tendency to consume all that is in their path, a small number of supermassive black holes (SMBHs) have been found to have high-speed jets of charged particles streaming from their cores.

These SMBHs are what power Active Galactic Nuclei, which are compact, bright regions that has been observed at the centers of particularly massive galaxies. At present, no one is certain how these SMBHs manage to fire off jets of hot matter. But it has been theorized that they could be caused by the accelerated rotational energy of the black holes themselves.

In keeping with this, the team considered the possibility that accreting X-ray sources could explain the escape of matter from a black hole. In other words, as a black hole’s intense gravity pulls matter inward, the black hole responds by spinning faster. As the hole’s gravitational pull increases, the speed creates energy, which inevitably causes charged particles to be pushed out. As Kaaret explained:

“As matter falls into a black hole, it starts to spin and the rapid rotation pushes some fraction of the matter out. They’re producing these strong winds that could be opening an escape route for ultraviolet light. That could be what happened with the early galaxies.”

Depiction of the tidal disruption event in F01004-2237. The release of gravitational energy as the debris of the star is accreted by the black hole leads to a flare in the optical light of the galaxy. Credit and copyright: Mark Garlick

Taking this a step further, the team hypothesized that this could be what was responsible for light escaping the “Dark Ages”. Much like the jets of hot material being emitted by SMBHs today, similarly massive black holes in the early Universe could have sped up due to the accretion of matter, spewing out light from the cloudiness and allowing for the Universe to become a clear, bright place.

In the future, the UI team plans to study Tol 1247-232 in more detail and locate other nearby galaxies that are also emitting ultraviolet light. This will corroborate their theory that black holes could be responsible for the observed point source of high-energy X-rays. Combined with studies of the earliest periods of the Universe, it could also validate the theory that the “Dark Ages” ended thanks to the presence of black holes.

Further Reading: Iowa Now, Monthly Notices of the Royal Astronomical Society