Discovery of a black hole in Andromeda

The discovery of a black hole enjoying a feeding frenzy in our nearest neighbor galaxy, Andromeda, has provided new insights into a mysterious class of extreme astrophysical objects called “ultraluminous X-ray sources”.
It isn’t unusual for material falling into a black hole to generate copious X-ray emission, but ultraluminous X-ray sources are so bright that they sometimes outshine their entire host galaxy in the X-ray band. Astronomers have spent years debating the nature of these enigmatic objects and two main scenarios have emerged. Either ultraluminous X-ray sources are unusually massive black holes feeding steadily on gas from an orbiting companion star, or alternatively they may be black holes around ten or twenty times as massive as our Sun that are somehow being force-fed by the in-falling gas.

This image shows the Andromeda galaxy (also known as M31) as seen in X-rays with ESA's XMM-Newton space observatory (shown here in red, green, blue and white, according to the energy of the different sources). This X-ray view is combined with an image of Andromeda taken with ESA's Herschel space observatory at far-infrared wavelengths (shown here in grey). Amongst the hundreds of X-ray sources revealed by XMM-Newton in Andromeda are: novae – binary systems comprising a white dwarf accreting material from a companion star; X-ray binaries – binary systems hosting a neutron star or a black hole accreting material from a companion star; and supernova remnants. The sequence of images at the top depict the centre of Andromeda and were taken with XMM-Newton on four occasions during 2012. These images illustrate the discovery of a new source, XMMU J004243.6+412519 (highlighted with a circle). XMMU J004243.6+412519 was first detected on 15 January 2012 within an XMM-Newton survey of Andromeda, designed to study the X-ray source population of this galaxy with particular emphasis on novae. On 21 January 2012, XMM-Newton recorded a significant brightening of this source; with a luminosity in excess of 10^39 erg/s, it was classified as an ultra-luminous X-ray source, or ULX. This is only the second ULX known in the Andromeda galaxy. The source then became fainter, as shown in the last image of the sequence, taken on 8 August 2012. XMMU J004243.6+412519 is an X-ray binary system consisting of a stellar-mass black hole that is accreting matter from a low-mass companion star. The source's dramatic boost in X-rays indicates a transition to an accretion rate close to the black hole's Eddington limit, or even above it. Credit: ESA/XMM-Newton/MPE


By using a number of Earth-orbiting X-ray telescopes, including NASA’s Swift and Fermi satellites, as well as the European Space Agency’s XMM-Newton observatory, a large international team of astronomers were able to watch as the X-ray emission from a black hole in the Andromeda galaxy – over 2 million light years away – brightened dramatically and then faded again over the course of 6 months during early 2012.
This pattern of X-ray emission is very reminiscent of behaviour that is exhibited by relatively low mass black holes found in our own galaxy – the Milky Way – when they are suddenly flooded by fresh material from their companion star. As they swallow the deluge of in-falling gas, these black holes also launch powerful beams of magnetized plasma called jets, which stream outwards at speeds close to that of light, and shine brightly at radio wavelengths.
Discovering such radio jets from an ultraluminous X-ray source provides a clear indication that these are just normal, everyday black holes.
To search for these telltale relativistic jets, the team trained the US National Science Foundation’s Karl G. Jansky Very Large Array on the black hole, and detected extremely bright, rapidly varying radio emission that dropped by a factor of two within just half an hour. This rapid variability tells us that the region producing radio waves is extremely small in size; no further across than the distance between Jupiter and the Sun.
This surprising finding was confirmed by zooming in using a super-high-resolution radio telescope called the Very Long Baseline Array. Despite the large distance to Andromeda, the absence of dust and gas in that direction allows an unimpeded view of the extreme astrophysical processes occurring in black hole’s immediate surroundings. In fact, this is the first time that radio jets have been detected from such a low mass black hole outside our own galaxy.
The research was published in the scientific journal Nature.
M. J. Middleton, et al., “Bright radio emission from an ultraluminous stellar-mass microquasar in M31”, Nature, 2012. DOI: 10.1038/nature11697

– Hugh Dickinson

This movie shows the Andromeda galaxy (also known as M31) as seen in X-rays with ESA's XMM-Newton space observatory (shown here in red, green, blue and white, according to the energy of the different sources). This X-ray view is combined with an image of Andromeda taken with ESA's Herschel space observatory at far-infrared wavelengths (shown here in grey). A series of observations taken with XMM-Newton in 2012 illustrate the discovery of a new source, XMMU J004243.6+412519. In the image for 7 January 2012, the new source is not yet visible. The source was first detected on 15 January 2012 and it can be seen in the upper part of the frame. About ten days after its discovery, XMMU J004243.6+412519 underwent a dramatic brightness boost, which can be seen in the images from 21 January and 31 January 2012. With a luminosity in excess of 10^39 erg/s, XMMU J004243.6+412519 was classified as an ultra-luminous X-ray source, or ULX. This is only the second ULX known in the Andromeda galaxy. The source then became fainter, as shown in the last two images of the sequence, from 28 July and 8 August 2012. Note that the field of view in these latter two images is slightly different to the earlier images. XMMU J004243.6+412519 is an X-ray binary which consists of a stellar-mass black hole that is accreting matter from a low-mass companion star. The source's dramatic boost in X-rays indicates a transition to an accretion rate close to the black hole's Eddington limit, or even above it. Other X-ray sources visible in the images are: novae – binary systems comprising a white dwarf accreting material from a companion star; X-ray binaries – binary systems hosting a neutron star or a black hole accreting material from a companion star; and supernova remnants. Credit: ESA/XMM-Newton/MPE

This movie shows the Andromeda galaxy (also known as M31) as seen in X-rays with ESA's XMM-Newton space observatory (shown here in red, green, blue and white, according to the energy of the different sources). This X-ray view is combined with an image of Andromeda taken with ESA's Herschel space observatory at far-infrared wavelengths (shown here in grey).

A series of observations taken with XMM-Newton in 2012 illustrate the discovery of a new source, XMMU J004243.6+412519.

In the image for 7 January 2012, the new source is not yet visible. The source was first detected on 15 January 2012 and it can be seen in the upper part of the frame. About ten days after its discovery, XMMU J004243.6+412519 underwent a dramatic brightness boost, which can be seen in the images from 21 January and 31 January 2012.

With a luminosity in excess of 10^39 erg/s, XMMU J004243.6+412519 was classified as an ultra-luminous X-ray source, or ULX. This is only the second ULX known in the Andromeda galaxy. The source then became fainter, as shown in the last two images of the sequence, from 28 July and 8 August 2012. Note that the field of view in these latter two images is slightly different to the earlier images.

XMMU J004243.6+412519 is an X-ray binary which consists of a stellar-mass black hole that is accreting matter from a low-mass companion star. The source's dramatic boost in X-rays indicates a transition to an accretion rate close to the black hole's Eddington limit, or even above it.

Other X-ray sources visible in the images are: novae – binary systems comprising a white dwarf accreting material from a companion star; X-ray binaries – binary systems hosting a neutron star or a black hole accreting material from a companion star; and supernova remnants.

Credit: ESA/XMM-Newton/MPE

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