Milky Way’s black hole twin discovered in nearby galaxy

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 26 January, 2009

Exploiting the Very Large Telescope’s acute infrared capabilities, astronomers have uncovered intense star-forming regions and a supermassive black hole in nearby galaxy NGC 253.

NGC 253 is shown here as observed with the WFI instrument, while the insert shows a close-up of the central parts as observed with the NACO instrument on ESO's Very Large Telescope and the ACS on the NASA/ESA Hubble Space Telescope. This unique set of observations has allowed astronomers to uncoveri many young, massive and dusty stellar nurseries as well as a twin of our own Milky Way's supermassive black hole. Image: ESO.

Measuring 70,000 light-years across and lying 13 million light years away, NGC 253 appears nearly edge-on from the Earth, and is one of the brightest and dustiest spiral galaxies known. Astronomers from the Instituto de Astrofísica de Canarias in Spain used ESO’s Very Large Telescope (VLT) and its adaptive optics instrument NACO (which corrects for the blurring effect introduced by the Earth's atmosphere that causes stars to twinkle) to discern a host of new young, massive and dusty stellar nurseries previously hidden within the galaxy, some with features just 11 light-years across.

"Our observations provide us with so much spatially resolved detail that we can, for the first time, compare them with the finest radio maps for this galaxy — maps that have existed for more than a decade," says Juan Antonio Fernández-Ontiveros, the lead author of the paper reporting the results in the Monthly Notices of the Royal Astronomical Society.

High resolution radio maps are comparatively easy to attain since radio waves are not affected by the turbulence of the atmosphere, and since radio waves have much longer wavelengths than visible light it is possible to combine observations from well-separated radio telescopes using interferometry. But the new observations allowed the astronomers to identify 37 distinct bright regions, a threefold increase on previous results, packed into a tiny region at the core of the galaxy, comprising just one percent of the galaxy's total size.

Close-up of the central regions of the starburst galaxy NGC 253. The bright regions are probably very active nurseries that contain as many as one hundred thousand young, massive stars bursting from their dusty cocoons. The field of view is 15 arcseconds. Image: ESO.

Furthermore, they suspect that there is a scaled-up version of Sagittarius A*, the bright radio source that lies at the core of the Milky Way and which we know harbours a massive black hole, lurking in the centre of NGC 253. "We have thus discovered what could be a twin of our Galaxy's centre," says Almudena Prieto.

Combining the NACO images with data from VISIR, another VLT instrument, as well as with images from the Hubble Space Telescope and radio observations made by the Very Large Array and the Very Large Baseline Interferometer, the astronomers painted a picture of the galaxy in different wavelengths, yielding clues as to the nature of the bright regions.

"We now think that these are probably very active nurseries that contain many stars bursting from their dusty cocoons," says Jose Antonio Acosta-Pulido. NGC 253 is known as a starburst galaxy, after its very intense star formation activity. The team report that each bright region could contain as many as one hundred thousand young, massive stars.

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