Category: Black Holes

For the first time, the most extreme collision to occur in the cosmos has been observed. Galaxies are known to hide supermassive black holes in their cores, and should the galaxies collide, tidal forces will cause massive disruption to the stars orbiting around the galactic cores. If the cores are massive enough, the supermassive black holes may become trapped in gravitational attraction. Do the black holes merge to form a super-supermassive black hole? Do the two supermassive black holes spin, recoil and then blast away from each other? Well, it would seem both are possible, but astronomers now have observational evidence of a black hole being blasted away from its parent galaxy after colliding with a larger cousin.

Most galaxies in the observable universe contain supermassive black holes in their cores. We know they are hiding inside galactic nuclei as they have a huge gravitational dominance over that region of space, sucking away at stars orbiting too close. Recent observations of galactic cores show quickly rotating stars around something invisible. Calculating the star orbital velocities, it has been deduced that the invisible body they are orbiting is something very massive; a supermassive black hole of hundreds of millions of solar masses. They are also the source of bright quasars in active, young galaxies.

Now, the same research group who made the astounding discovery of the structure of a black hole molecular torus by analysing the emission of echoed light from an X-ray flare (originating from star matter falling into the supermassive black hole’s accretion disk) have observed one of these supermassive black holes being kicked out of its parent galaxy. What caused this incredible event? A collision with another, bigger supermassive black hole.

Stefanie Komossa and her team from the Max Planck Institute for extraterrestrial Physics (MPE) made the discovery. This work, to be published in Astrophysical Journal Letters on May 10th, verifies something that has only been modelled in computer simulations. Models predict that as two fast-rotating black holes begin to merge, gravitational radiation is emitted through the colliding galaxies. As the waves are emitted mainly in one direction, the black holes are thought to recoil – much like the force that accompanies firing a rifle. The situation can also be thought of as two spinning tops, getting closer and closer until they meet. Due to their high angular momentum, the tops experience a “kick”, very quickly ejecting the tops in the opposite directions. This is essentially what two supermassive black holes are thought to do, and now this recoil has been observed. What’s more, the ejected black hole’s velocity has been measured by analysing the broad spectroscopic emission lines of the hot gas surrounding the black hole (its accretion disk). The ejected black hole is travelling at a velocity of 2650 km/s (1647 mi/s). The accretion disk will continue to feed the recoiled black hole for many millions of years on its journey through space alone.

Supporting the evidence that this is indeed a recoiling supermassive black hole, Komossa analysed the parent galaxy and found hot gas emitting X-rays from the location where the black hole collision took place.

Now Komossa and her team hope to answer the questions this discovery has created: Did galaxies and black holes form and evolve jointly in the early Universe? Or was there a population of galaxies which had been deprived of their central black holes? And if so, how was the evolution of these galaxies different from that of galaxies that retained their black holes?

It is hoped that the combined efforts of observatories on Earth and in space may be used to find more of these “superkicks” and begin to answer these questions. The discovery of gravitational waves will also help, as this collision event is predicted to wash the Universe in powerful gravitational waves.

Source: MPE News

The consequences of two black holes colliding may be huge, the energy produced by such a collision could even be detected by observatories here on Earth. Ripples in space-time will wash over the Universe as gravitational waves and are predicted to be detected as they pass through the Solar System. Taking this idea one step further, what would happen if three black holes collide? Sound like science fiction? Well it’s not, and there is observational evidence that three black holes can cluster together, possibly colliding after some highly complex orbits that can only be calculated by the most powerful computers available to researchers…


Back in January 2007, a quasar triplet was observed over 10 billion light years away. Quasars are generated by the supermassive black holes eating away at the core of active galaxies. Using the powerful W. M. Keck Observatory, researchers from Caltech were able to peer back in time (10 billion years) to see a period in the Universe’s life when active galaxies and black hole mergers would have been fairly common events (when compared to the calmer Universe of today). They observed three tightly packed quasars, an unprecedented discovery.

Now, scientists Manuela Campanelli, Carlos Lousto and Yosef Zlochower, all working at Rochester Institute of Technology’s Center for Computational Relativity and Gravitation, have simulated the highly complex mechanisms behind three interacting and merging supermassive black holes, much like the situation observed by Keck in 2007. The same group have worked on calculating the collision of two black holes before and have written a code that is powerful enough to simulate the collision of up to 22 black holes. However, 22 black holes probably wouldn’t collide naturally, this simply demonstrates the stability of the code, “Twenty-two is not going to happen in reality, but three or four can happen,” says Yosef Zlochower, an assistant professor. “We realized that the code itself really didn’t care how many black holes there were. As long as we could specify where they were located – and had enough computer power – we could track them.”

These simulations are of paramount importance to the gravitational wave detectors such as the Laser Interferometer Gravitational-Wave Observatory (LIGO). So far there has been no firm evidence to come from these detectors, but more time is needed, the LIGO detector requires several years of “exposure time” to collect enough data and remove observational “noise”. But what do gravitational wave astronomers look for? This is the very reason many different cosmic scenarios are being simulated so the characteristics of events like two or three black holes mergers can be identified from their gravitational wave signature.

Gravitational wave astronomers “need to know what to look for in the data they acquire otherwise it will look like just noise. If you know what to look for you can confirm the existence of gravitational waves. That’s why they need all these theoretical predictions.” – Manuela Campanelli, director of RIT’s Center for Computational Relativity and Gravitation.

Source: RIT University News

According to new research, a galaxy with a quasar in the middle is not a good place to grow up. As active galactic nuclei (AGN) evolve, they pass through a “quasar phase”, where the accretion disk surrounding the central black hole blasts intense radiation into space. The quasar far outshines the entire host galaxy. After the quasar phase, when the party is over, it is as if there is no energy left and star formation stops.

AGN are the compact, active and bright central cores to active galaxies. The intense brightness from these active galactic cores is produced by the gravitationally driven accretion disk of hot matter spinning and falling into a supermassive black hole at the centre. During the lifetime of an AGN, the black hole/accretion disk combo will undergo a “quasar phase” where intense radiation is blasted from the superheated gases surrounding the black hole. Typically quasars are formed in young galaxies.

Although the quasar phase is highly energetic and tied with young galaxy formation, according to new results from the Sloan Digital Sky Survey, it also marks the end for any further star birth in the galaxy. These findings will be presented today (Friday 4th April) at the RAS National Astronomy Meeting in Belfast, Northern Ireland, by Paul Westoby having just completed a study of 360 000 galaxies in the local Universe. He carried out this research with Carole Mundell and Ivan Baldry from the Astrophysics Research Institute of Liverpool, John Moores University, UK. This study was proposed to understand the relationship between accreting black holes, the birth of stars in galactic cores and the evolution of galaxies as a whole. The results are astonishingly detailed.

By analysing so many galaxies, quite a detailed picture emerges. The primary result to come from this shows that as a young galactic core is dominated by a highly energetic quasar, star formation stops. After this phase in a galaxy’s life, star formation is not possible; the remaining stars are left to evolve by themselves.

It is believed that all AGNs go through the quasar phase in their early galactic lives. It is also thought that most massive galaxies will have a supermassive black hole hiding inside their galactic cores passively, having already gone through the quasar phase. Westoby notes that some dormant supermassive black holes can be “reignited” into a secondary quasar phase, but the mechanisms behind this are sketchy.

“The starlight from the host galaxy can tell us much about how the galaxy has evolved […] Galaxies can be grouped into two simple colour families: the blue sequence, which are young, hotbeds of star-formation and the red sequence, which are massive, cool and passively evolving..” – Paul Westoby.

It is found there is a sudden cut-off point for star formation, and this occurs right after the quasar phase. After the quasar phase, the AGN relaxes into a quieter state, there is no star formation and gradual evolution of stars progresses into the “red sequence” of star evolution.

Other findings include the indication that regardless of the size of the galaxy, it is the shape of the galactic “bulge” that matters. Without a large classical bulge in the centre, supermassive black holes that drive the AGN are not possible. Therefore, only galaxies with a bulge have AGN at the core. Another factor affecting supermassive black hole formation is the density of galaxies in a volume of space. Should there be too many, supermassive black holes become a scarcity.

Source: The RAS National Astronomy Meeting 2008

Black holes seem to have no upper limit; some weigh in at hundreds of millions of times the mass of the Sun. But how small can they be? Astronomers have discovered what they think is the least massive black hole ever seen, with a mere 3.8 times the mass of the Sun, and a diameter of only 25 km (15 miles) across.

The announcement was made by Nikolai Shaposhnikov of NASA’s Goddard Space Flight Center and his colleagues at the American Astronomical Society High-Energy Astrophysics Division currently being held in Los Angeles, California.

The “tiny” black hole, known as XTE J1650-500, was discovered back in 2001 in a binary system with a normal star. Astronomers had known about the binary system for several years, but they were finally able to make accurate measurements using NASA’s Rossi X-ray Timing Explorer (RXTE) to pin down the mass.

Although black holes themselves are invisible, they’re often surrounded by a disk of hot gas and dust – material chokes up, like water going down the drain. As the hot gas builds up, it releases torrents of X-rays at regular intervals.

Astronomers have long suspected that the frequency of these X-ray blasts depend on the mass of the stars. As the mass of the black hole increases, the size of the accretion disk expands outward too; there are less frequent X-ray emissions.

By cross referencing this method with other, established techniques for weighing black holes, the team is very confident that they’ve got the trick to measuring black hole mass.

When they applied their technique to XTE J1650-500, they turned up a mass of 3.8 Suns, give or take half a solar mass. This is dramatically smaller than the previous record holder at 6.3 Suns.

What’s the smallest possible black hole? Astronomers think it’s somewhere between 1.7 and 2.7 solar masses. Smaller than that and you get a neutron star. Finding black holes that approach this lower limit will help physicists better understand how matter behaves when its crushed down in this extreme environment.

Original Source: NASA News Release