Image of the Day: Fiery Remnants of Cosmic Objects Ripped Apart by Milky Way’s Supermassive Black Hole

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"Observations like this [image], over a range of wavelengths, are really the only way to understand what's going on close to the black hole," says Andreas Eckart of the University of Cologne, who led the team.

Sagittarius A*, located at the center of our own Milky Way Galaxy at a distance from Earth of about 26, 000 light-years, is a supermassive black hole with a mass of about four million times that of the Sun.


"Sagittarius A* is unique, because it is the nearest of these monster black holes, lying within our own galaxy," explains team member Frederick K. Baganoff of the MIT. "Only for this one object can our current telescopes detect these relatively faint flares from material orbiting just outside the event horizon."

The emission from Sagittarius A* is thought to come from gas thrown off by stars, which then orbits and falls into the black hole.

Making the simultaneous observations required careful planning between teams at the two telescopes. After several nights waiting at the two observatory sites, they struck lucky.

"At the VLT, as soon as we pointed the telescope at Sagittarius A* we saw it was active, and getting brighter by the minute. We immediately picked up the phone and alerted our colleagues at the APEX telescope," says Gunther Witzel, a PhD student from the University of Cologne.

Macarena García-Marín, also from Cologne, was waiting at APEX, where the observatory team had made a special effort to keep the instrument on standby. "As soon as we got the call we were very excited and had to work really fast so as not to lose crucial data from Sagittarius A*. We took over from the regular observations, and were in time to catch the flares," she explains.

Over the next six hours, the team detected violently variable infrared emission, with four major flares from Sagittarius A* . The submillimetre-wavelength results also showed flares, but, crucially, this occurred about one and a half hours after the infrared flares.

The researchers explain that this time delay is probably caused by the rapid expansion, at speeds of about 5 million km/h, of the clouds of gas that are emitting the flares. This expansion causes changes in the character of the emission over time, and hence the time delay between the infrared and submillimetre flares.

Although speeds of 5 million km/h may seem fast, this is only 0.5% of the speed of light. To escape from the very strong gravity so close to the black hole, the gas would have to be travelling at half the speed of light –– 100 times faster than detected –– and so the researchers believe that the gas cannot be streaming out in a jet. Instead, they suspect that a blob of gas orbiting close to the black hole is being stretched out, like dough in a mixing bowl, and this is causing the expansion.

The simultaneous combination of the VLT and APEX telescopes has proved to be a powerful way to study the flares at multiple wavelengths. The team hope that future observations will let them prove their proposed model, and discover more about this mysterious region at the centre of our Galaxy.

The false-color image below shows the central region of our Milky Way Galaxy as seen by Chandra. The bright, point-like source at the center of the image was produced by a huge X-ray flare that occurred in the vicinity of the supermassive black hole at the center of our galaxy. This central black hole has about 2.6 million times the mass of our Sun and is associated with the compact radio source Sagittarius A*.

During the observation the X-ray source at the galactic center brightened dramatically in a few minutes, and after about 3 hours, rapidly declined to the pre-flare level. The rapid variation in X-ray intensity indicates that the flare was due to material as close to the black hole as the Earth is to the Sun. This is the most compelling evidence yet that matter falling toward the black hole is fueling energetic activity in the galactic center.

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Image credit: NASA/MIT/F.Baganoff et al.

Source: ESO

Image credit: ESO/APEX/2MASS/A. Eckart et al.

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