XMM-Newton Uncovers Well-Tuned Super-Massive Black Hole

XMM-Newton has uncovered a well-tuned periodic signal from a super-massive black hole lodged at the centre of a galaxy, ending a long quest for such an object. The discovery provides scientists with a clearer picture on black hole accretion processes and an excellent tool to study active galactic nuclei (AGNs).
These periodic signals originating from the black hole are emitted in X-rays, which are blocked out by the Earth's atmosphere. So the team used data from ESA's orbiting X-ray observatory, XMM-Newton, to make the discovery.
The super-massive black hole, whose signals XMM-Newton has overheard, is located at the centre of a galaxy that goes by the ungainly name RE J1034+396. The black hole itself is estimated to be a million times as massive as our Sun.
In theory, as matter is sucked in to a black hole, it is heated up, and emits X-rays. The X-ray emission can then be modulated at a certain frequency, as infalling matter wobbles around the black hole, and this frequency is detected as a periodic signal.
From the frequency of the signal, it is possible to estimate the size of the black hole itself. These periodic signals are widely observed in black holes of a lower mass, of the order of tens of solar masses, in our Galaxy.
Scientists have suspected that the underlying physical processes behind black hole accretion mechanisms are the same, regardless of the size of the black hole. This means that such periodic signals should also be emitted by super-massive black holes lodged at the galactic centres, also called active galactic nuclei. But until now, no super-massive black hole was known to display such a periodic signal.
XMM-Newton's sensitive instruments have now shown that the black hole at the centre of RE J1034+396 displays a periodic signal (called a quasi-periodic oscillation), once per hour.
The finding confirms that the fundamental physical processes behind black hole accretion mechanisms are the same, giving them a new, powerful tool to study AGN.
"With the observation of these well-tuned signals, we know for sure that an increase of even a million times in the mass of the black hole doesn't seem to change the basic process by which gas is pulled into it," said Dr Marek Gierlinski of the University of Durham, lead author of the paper in which the findings are reported.
"This long-awaited discovery has been made possible with XMM-Newton's highly sensitive instruments. We are thrilled that the mission has made a fundamental contribution to our understanding of these complex systems," said Norbert Schartel, ESA's XMM-Newton Project Scientist.
Now the quest is on to find out why some black holes show this behaviour and others don't, and to learn more about how matter behaves just before it falls into a black hole.

VLT And Rossi XTE Satellite Probe Violently Variable Black Holes

Unique observations of the flickering light from the surroundings of two black holes provide new insights into the colossal energy that flows at their hearts.
By mapping out how well the variations in visible light match those in X-rays on very short timescales, astronomers have shown that magnetic fields must play a crucial role in the way black holes swallow matter.
Like the flame from a candle, light coming from the surroundings of a black hole is not constant - it flares, sputters and sparkles. "The rapid flickering of light from a black hole is most commonly observed at X-ray wavelengths," says Poshak Gandhi, who led the international team that reports these results.
"This new study is one of only a handful to date that also explore the fast variations in visible light, and, most importantly how these fluctuations relate to those in X-rays."
The observations tracked the shimmering of the black holes simultaneously using two different instruments, one on the ground and one in space. The X-ray data were taken using NASA's Rossi X-ray Timing Explorer satellite.
The visible light was collected with the high speed camera ULTRACAM, a visiting instrument at ESO's Very Large Telescope (VLT), recording up to 20 images a second. ULTRACAM was developed by team members Vik Dhillon and Tom Marsh. "These are among the fastest observations of a black hole ever obtained with a large optical telescope," says Dhillon.
To their surprise, astronomers discovered that the brightness fluctuations in the visible light were even more rapid than those seen in X-rays.
In addition, the visible-light and X-ray variations were found not to be simultaneous, but to follow a repeated and remarkable pattern: just before an X-ray flare the visible light dims, and then surges to a bright flash for a tiny fraction of a second before rapidly decreasing again.
None of this radiation emerges directly from the black hole, but from the intense energy flows of electrically charged matter in its vicinity.
The environment of a black hole is constantly being reshaped by a riotous m阬ee of strong and competing forces such as gravity, magnetism and explosive pressure. As a result, light emitted by the hot flows of matter varies in brightness in a muddled and haphazard way.
"But the pattern found in this new study possesses a stable structure that stands out amidst an otherwise chaotic variability, and so, it can yield vital clues about the dominant underlying physical processes in action," says team member Andy Fabian.
The visible-light emission from the neighbourhoods of black holes was widely thought to be a secondary effect, with a primary X-ray outburst illuminating the surrounding gas that subsequently shone in the visible range. But if this were so, any visible-light variations would lag behind the X-ray variability, and would be much slower to peak and fade away.
"The rapid visible-light flickering now discovered immediately rules out this scenario for both systems studied," asserts Gandhi. "Instead the variations in the X-ray and visible light output must have some common origin, and one very close to the black hole itself."
Strong magnetic fields represent the best candidate for the dominant physical process. Acting as a reservoir, they can soak up the energy released close to the black hole, storing it until it can be discharged either as hot (multi-million degree) X-ray emitting plasma, or as streams of charged particles travelling at close to the speed of light.
The division of energy into these two components can result in the characteristic pattern of X-ray and visible-light variability. The two black holes studied here, GX 339-4 and SWIFT J1753.5-0127, are the remnants of massive dead stars in the Milky Way.
They are embedded in separate "binary" stellar systems, where the black hole is bound to a normal star that is losing matter to its dark companion. Both black holes have masses of around ten times that of our Sun, yet the size of their orbits is only a few million kilometres, much more compact than the orbit of Mercury around our Sun.
Apart from Gandhi, Dhillon, Durant, Fabian, and Marsh, the other members of the team are Kazuo Makishima at the University of Tokyo, Japan, Jon Miller at the University of Michigan, USA, Tariq Shahbaz at the Instituto de Astrofisica de Canarias, Spain, and Henk Spruit of the Max-Planck-Institute for Astrophysics, Germany.