The turbulent past of the Milky Way's black hole

May 28, 2010
XMM-Newton images of the emission of the neutral iron fluorescent line in the molecular clouds around Sgr A* (Bridge, MC1 et MC2) between 2004 and 2008. The progression of the emission in the sub-regions indicated by ellipses 1,2, 3, and 4 of The Bridge are clearly shown. The distance traveled by the emission is 15 light years in less than 5 years. The angular scale (2 arc-minutes = 15 light years at the distance of the galactic center) and the direction towards Sgr A* are also shown. (c) Ponti G., et al., 2010, The Astrophysical Journal, V. 714, p. 732-747

The supermassive black hole at the center of our Galaxy went through turbulent times over the past centuries. We know this thanks to its surrounding molecular clouds, whose varying X-ray and gamma-ray luminosity reflects a major flare in the past. These findings, obtained by an international team of researchers led by French astrophysicists, are published in The Astrophysical Journal.

The located in usually show intense activity. But this is not true of our own Galaxy's black hole, Sgr A*, which shows very low activity. However, an international team of researchers, led by astrophysicists from the Astroparticle and Laboratory in Paris, has succeeded in showing that the black hole was active in the very recent past, and that it is therefore not as unusual as it seemed.

XMM-Newton and INTEGRAL, two ESA satellites to which CNES, CEA and CNRS-INSU have made a major contribution, have enabled researchers to observe X-ray and gamma-ray emissions from in the region of the galactic center, near Sgr A*. The scientists were surprised to discover that the emissions showed spectacular variation, such as the progressive brightening of one of the clouds between 2004 and 2009, at an apparent speed three times greater than that of light (see Fig. 1).

The phenomenon shows that the clouds reflect the high-energy radiation produced by the intense activity of the supermassive black hole. The light echo that reaches us is delayed in comparison with the direct light from the black hole. This delay depends on the position of the cloud and on the time the radiation takes to travel the distance from the black hole to the cloud. By observing the decay of the gamma-ray emission from another cloud (Fig. 2), the researchers estimated the duration and intensity of the flare, which began around four centuries ago and ended at the beginning of the twentieth century. For three hundred years, our Galaxy's supermassive black hole was therefore a million times brighter than now.

Explore further: The entropy of black holes

More information: ArXiv paper: arxiv.org/abs/1005.4807

add to favorites email to friend print save as pdf

Related Stories

Astronomers shed surprising light on our galaxy's black hole

Jan 10, 2006

In the most comprehensive study of Sagittarius A* (Sgr A*), the enigmatic supermassive black hole in the center of the Milky Way Galaxy, astronomers -- using nine ground and space-based telescopes including the Hubble Space ...

How do supermassive black holes get so big?

Apr 26, 2010

(PhysOrg.com) -- At the center of most galaxies lie supermassive black holes that can grow to become more than a billion times larger than our Sun. However, astrophysicists don’t fully understand the formation ...

Nearby black hole is feeble and unpredictable

May 25, 2010

For over 10 years, NASA's Chandra X-ray Observatory has repeatedly observed the Andromeda Galaxy for a combined total of nearly one million seconds. This unique data set has given astronomers an unprecedented ...

An Intriguing, Glowing Galaxy

May 14, 2009

A supermassive black hole may be responsible for the glowing appearance of galaxy 3C 305, located about 600 million light years away in the constellation Draco. Composite data from NASA’s Chandra X-ray Observatory ...

Active galaxies are different near and far

Jan 06, 2009

(PhysOrg.com) -- An ongoing X-ray survey undertaken by NASA's Swift spacecraft is revealing differences between nearby active galaxies and those located about halfway across the universe. Understanding these ...

Recommended for you

The entropy of black holes

Sep 12, 2014

Yesterday I talked about black hole thermodynamics, specifically how you can write the laws of thermodynamics as laws about black holes. Central to the idea of thermodynamics is the property of entropy, which c ...

Modified theory of dark matter

Sep 12, 2014

Dark matter is an aspect of the universe we still don't fully understand. We have lots of evidence pointing to its existence (as I outlined in a series of posts a while back), and the best evidence we have point ...

Gaia discovers its first supernova

Sep 12, 2014

(Phys.org) —While scanning the sky to measure the positions and movements of stars in our Galaxy, Gaia has discovered its first stellar explosion in another galaxy far, far away.

Astronomers unveil secrets of giant elliptical galaxies

Sep 12, 2014

New findings of how giant elliptical galaxies move have been discovered by an international team of astronomers using the newly installed Multi Unit Spectroscopic Explorer (MUSE) at the European Southern Observatory's (ESO) ...

Exploring the cosmic X-ray background

Sep 12, 2014

You are likely familiar with the cosmic microwave background. This background is a thermal remnant of the big bang. Because of the expansion of the universe, this remnant energy has a temperature of about ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

yyz
5 / 5 (1) May 28, 2010
Might these observations of a x-ray light echo from Sag A* provide a similar explanation for the x-ray brightening seen in M 31*? [http://www.physor...880.html ] It seems possible that a previous outburst of M 31* is only now (post Jan 2006) illuminating a nearby cloud.

That story opines "The overall brightening since 2006 could be caused by M31* capturing winds from an orbiting star, or by a gas cloud that spiraled into the black hole. The increase in the rate of material falling towards the black hole is thought to drive an X-ray brightening of a relativistic jet." but also notes "We have some ideas about what's happening right around the black hole in Andromeda, but the truth is we still don't really know the details," Curious.
Thecis
not rated yet May 31, 2010
Just a thing that bothers me... "at an apparent speed three times greater than that of light (see Fig. 1)".
First, nothing that we know of can be faster than the speed of light (gossip not taken into account). So how can it appear to be faster?
yyz
5 / 5 (1) May 31, 2010
These apparent superluminal speeds are an illusion caused by the geometry of the expanding light echo. The speed of light remains a constant and no laws are broken. Check out 'light echo': http://en.wikiped...ght_echo
Thecis
not rated yet Jun 09, 2010
Hi yyz,
thanks for the clarification.
Although I have read the link, it is still a bit fuzy to me. However, the general idea is clear.