Tag Archives: Supermassive

Supermassive Black Hole.

Supermassive black holes like to wear gas donuts — and we found out why

Supermassive black holes don’t really form dust ‘donuts’ — the structures surrounding these bodies are more akin to galactic matter fountains, new research reveals.

Supermassive Black Hole.

Artist’s concept of a supermassive black hole. Also shown are the accretion disk (donut) and the outflowing jet of energetic particles.
Image credits NASA-JPL.

Computer simulations and new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) suggest that the gas accretion rings around supermassive black holes (SBH) aren’t ring-shaped at all. Instead, gas being expelled from the SBM interacts with infalling matter to create a complex circulation pattern — one which the authors liken to a fountain.

Jets of matter

Most galaxies revolve around a SBH. These objects can be millions, even billions of times as heavy as the Sun, and they knit together galaxies through sheer gravitational power. Some of these SBHs are actively consuming new material. So far, common wisdom held that instead of falling directly in, matter builds around an active black hole in a donut or ring-shaped structure.

It wasn’t far from the truth but, new research reveals, it wasn’t spot-on either. A study led by Takuma Izumi, a researcher at the National Astronomical Observatory of Japan (NAOJ), reports that this ‘donut’ is not actually a rigid structure, rather a complex collection of highly dynamic gaseous components.

The researchers used the ALMA telescope to observe the Circinus Galaxy and the SBH at its center — which is roughly 14 million light-years away from Earth. They then compared their observations to computer models of gas falling toward a black hole. These simulations were run using the Cray XC30 ATERUI supercomputer operated by NAOJ.

All in all, the team found that there’s a surprising level of interplay between the gases in this structure. Cold molecular gas first falls towards the black hole to form a disk near the plane of rotation. Being so close to a black hole heats up the gas until its atoms break apart into protons and electrons. Not all of these products go on to be swallowed by the black hole. Some are instead expelled above and below the disk but are then snagged by the SBH’s immense gravitational presence, falling back onto the disk.

SBH interaction.

Rough schematic of the process’ dynamics. Pc stands for parsec, equal to about 3.26 light-years (30 trillion km or 19 trillion miles).

These three components circulate continuously, the team explains. Their interaction creates three-dimensional flows of highly turbulent matter around the black hole.

“Previous theoretical models set a priori assumptions of rigid donuts,” explains co-author Keiichi Wada, a theoretician at Kagoshima University in Japan who lead the simulation study.

“Rather than starting from assumptions, our simulation started from the physical equations and showed for the first time that the gas circulation naturally forms a donut. Our simulation can also explain various observational features of the system.”

The team says their paper finally explains how donut-shaped structures form around active black holes and, according to Izumi, will “rewrite the astronomy textbooks.”

The paper ” Circumnuclear Multiphase Gas in the Circinus Galaxy. II. The Molecular and Atomic Obscuring Structures Revealed with ALMA” has been published in The Astrophysical Journal.

Supermassive black hole spotted struggling with its galactic meal

Even supermassive black holes can bite off more than they can chew, it seems, based on observations of a nearby pair of colliding galaxies.

Messier51_sRGB.

NGC 5194 & 5195.
Image credits NASA, ESA.

A study analyzing emissions throughout the electromagnetic spectrum released by a nearby supermassive black hole gobbling up matter has revealed that even they can suffer from ‘indigestion’.

The mammoth body, weighing in at some 19 million times the mass of the Sun, lies at the center of a small galaxy named NGC 5195. Once every few hundred millions of years, NGC 5195 collides with the outer arms of its larger neighbor, known as NGC 5194 or (the more palatable) ‘Whirlpool’ galaxy. This happens because the two are locked in a gravitational wooing period that — in a few billion more years — will see them merge into a single galaxy.

But in the meantime, when these two galaxies touch, the supermassive black hole at the center of NGC 5195 picks up a lot of matter from Whirlpool into an accretion disk — so much matter, in fact, that it can’t absorb it all. But it still collapses onto the black hole since it’s subjected to enormous gravity. So all that excess matter eventually gets blown out into space. Last year, NASA’s Chandra X-Ray Observatory caught a whiff of X-ray emission that appeared to result from this process, but we didn’t really understand the how it happens.

Now, using high-resolution images of NGC 5195’s core taken with the e-MERLIN radio array, and drawing from archive images of the area taken with the Very Large Array (VLA), Chandra and the Hubble Space Telescope, a team of astronomers at the University of Manchester’s Jodrell Bank Centre for Astrophysics revealed the details of how these huge blasts of matter occur, and their behavior in space.

Letf: Image of the Whirlpool galaxy and NGC 5195.
Right: False colour image of NGC 5195 created by combining the VLA 20 cm radio image (red), the Chandra X-ray image (green), and the Hubble Space telescope H-alpha image (blue).
Image credits Jon Christensen.

They report that when the accretion disk surrounding NGC 5195’s supermassive black hole breaks down, the immense forces and pressures involved create a shock wave which blasts all that matter back out into space — if you’re thinking this is kinda like how supernovae form, you’re pretty much on point.

Electrons, accelerated by this event close to the speed of light, interact with magnetic fields from neighboring bodies and emit energy in the radio wavelength spectrum. The X-ray emissions e-MERLIN picked up are created when the shock wave hits the gasses in the interstellar medium, inflating and heating them up. This process strips electrons from hydrogen gas atoms and ionizes them, creating the features seen by Chandra and Hubble.

“Comparing the VLA images at radio wavelengths to Chandra’s X-ray observations and the hydrogen-emission detected by Hubble, shows that features are not only connected, but that the radio outflows are in fact the progenitors of the structures seen by Chandra and Hubble,” explains Dr Hayden Rampadarath, who will be presenting his findings at the National Astronomy Meeting at the University of Hull explains.

“This is an event of galactic proportions that we can see right across the electromagnetic spectrum.”

According to him, the arcs seen in the NGC 5195 system are 1 to 2 million years old, meaning the first bits of matter were being pushed away from the black hole at about the same time as humans were learning how to make fire.

This isn’t the first time we’ve seen a black hole struggling to eat everything on its plate, and that event also had many of the features Dr Rampadarath identified here. Knowing this, it may be easier to spot overly-greedy black holes in the future.

Researchers found a supermassive black hole choking on its meal

Scientists have found a supermassive black hole that seems to have bit more than it can chew. At the center of a galaxy some 300 million light years away from Earth, the black hole is straining to absorb the mass of a star it recently collapsed, “chocking” on its remains.

Artist’s impression of a supermassive black hole at a galaxy’s center. The blue color represents radiation pouring out from material very close to the black hole.
Image credits NASA/JPL-Caltech.

A team of researchers including members from MIT and NASA’s Goddard Space Flight Center have recently reported picking up on a peculiar “tidal disruption flare”, a massive burst of electromagnetic energy released when a black hole collapses a hapless star. The flare, named ASASSN-14li, first hit our sensors on Nov. 11, 2014, and researchers have since pointed all kinds of telescopes towards the source to learn as much as possible about how black holes evolve.

Led by MIT postdoc at the Kavli Institute for Astrophysics and Space Research Dheeraj Pasham, the team looked at data obtained with two different telescopes and found a strange pattern in the energy levels of the flare. As the supermassive black hole (I’ll just call it a SBH from not on) first began absorbing the former star’s matter, the team picked up on slight variations in the visible and ultraviolet intervals of the electromagnetic spectrum. Which in itself isn’t that weird — we’ll get to it in a moment. But the same pattern of fluctuations was picked up again 32 days later, this time in the X-ray band.

A flare of gluttony

So first off let’s get to know what these flares are and how they usually behave.

As I’ve said, tidal disruption flares are huge bursts of energy released when a black hole’s immense gravitational pull rips a star apart. The bursts propagate all over the electromagnetic spectrum, from radio, visible, and UV all the way to X-ray and gamma ray intervals. They’re pretty rare, so we didn’t witness that many of them despite the fact that they really stand out. But when we do, it’s a dead give away for hidden black holes — which would be almost impossible to spot otherwise.

“You’d have to stare at one galaxy for roughly 10,000 to 100,000 years to see a star getting disrupted by the black hole at the center,” Pasham, who’s also the paper’s first author, says.

“Almost every massive galaxy contains a supermassive black hole. But we won’t know about them if they’re sitting around doing nothing, unless there’s an event like a tidal disruption flare.”

So in a way we were lucky, but our sensors were also ready for it. The ASASSN-14li flare was picked up by the ASASSN (All Sky Automated Survey for SuperNovae) network of automated telescopes. Soon after, researchers pointed other telescopes towards the black hole, including the X-ray telescope aboard NASA’s Swift satellite — designed to monitor the sky for bursts of extremely high energy.

Artist’s rendering of the supermassive black hole that generated the flare and its accretion disk.
Image credits NASA / Swift / Aurore Simonnet, Sonoma State University.

“Only recently have telescopes started ‘talking’ to each other, and for this particular event we were lucky because a lot of people were ready for it,” Pasham says. “It just resulted in a lot of data.”

By looking at all the data they gathered on the event, Pasham and his team answered a long-standing mystery: where did these bursts of light originate in flares? By modeling a black hole’s dynamics, scientists have previously been able to explain that as a black hole rips its star apart, the resulting material can produce X-ray emissions very close to the event horizon. But the source for the visible and UV light proved elusive.

The team studied the 270 days after ASASSN-14li was first detected, with particular emphasis on the X-ray and optical/UV data taken by the Swift satellite and the Las Cumbres Observatory Global Telescope. Two broad peaks in the X-ray band were identified (one around day 50, and the other around day 110), and one short dip (around day 80). This was the exact same pattern they recorded for the visible/UV spectrum just 32 days earlier.

Their next step was to run simulations of the flare produced by a star collapsing next to a black hole and the resulting accretion disc (similar to how planets get them) — along with its presumed speed, size, and the rate which material falls onto the black hole.

Tug of war

 

The results suggest these energy fluctuations are a kind of electromagnetic echo. After the star was torn apart, its remains started swirling the supermassive black hole. As it drew nearer to the event horizon, the cloud of matter accelerated and became more tightly packed, releasing bursts of UV and visible light when its particles collided at high speeds. As the matter was pulled closer to the black hole it got even faster and denser, which also made it heat up. In this excited state of matter close to absorption into the event horizon, the collisions produced X- and gamma ray bursts instead of the lower-energy visible and UV bursts.

In the case of ASASSN-14li, this process happened much more slowly that usually because the great quantity of matter proved a bit too much for the black hole to chew in a single bite.

 

“In essence, this black hole has not had much to feed on for a while, and suddenly along comes an unlucky star full of matter.” Pasham explains. “What we’re seeing is, this stellar material is not just continuously being fed onto the black hole, but it’s interacting with itself — stopping and going, stopping and going. This is telling us that the black hole is ‘choking’ on this sudden supply of stellar debris.”

“For supermassive black holes steadily accreting, you wouldn’t expect this choking to happen. The material around the black hole would be slowly rotating and losing some energy with each circular orbit,” he adds.

“But that’s not what’s happening here. Because you have a lot of material falling onto the black hole, it’s interacting with itself, falling in again, and interacting again. If there are more events in the future, maybe we can see if this is what happens for other tidal disruption flares.”

The full paper “Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li” has been published in the journal Astrophysical Journal Letters.