A black hole named Edd

Posted by Francis Reddy
on Friday, January 11, 2008

Francis ReddyOne of the pleasures of attending American Astronomical Society meetings is strolling through a sea of poster papers. A poster paper is exactly what it sounds like — it’s an oversized page that summarizes the results of a single study.

Now and then, you spot displays where the science comes mixed with whimsy. Such is the case with “Discovery and Interpretation of an X-ray Period in the Galactic Center Source CXOGC J174536–2856,” a study led by Valerie Mikles at the University of Florida. The poster features art of a massive star blowing a dense stellar wind toward a putative black hole represented by … Godzilla. (PDF here; be warned, it’s large.)

Mikles and her colleagues nicknamed the object Edd-1, which is hardly your typical astronomical moniker. “It actually has no scientific significance whatsoever,” she says.

The story: She first presented this source in an earlier poster that included a picture of Edvard Munch's "The Scream."  “I used ‘The Scream’ because the iron line and the hydrogen lines are screamingly bright — the iron line is one of the largest ever seen,” Mikles explains. The line comes from iron atoms that have lost 24 electrons (FeXXV). “It’s stripped pretty bare,” she says.

So, the “Ed” in Edd-1 comes from Edvard. The second “d” is a pop-culture reference to “Ed, Edd n Eddy” on Cartoon Network. “That's why Edd-1 is a nickname and not an alternative name, like Cyg X-1,” Mikles notes.

It’s also lots easier to type than CXOGC J174536–2856.

After dealing with the nickname, the science is pretty straightforward. Observations using NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton reveal that Edd-1’s X-ray flux waxes and wanes over 189 days. That’s possibly an orbital period, and, if it is, the changes in brightness could occur because the X-ray source regularly becomes eclipsed. Alternatively, the changes might be due to variations in the fuel supply fed to an accreting object, like a neutron star or a black hole.

Combined with infrared observations taken with NASA’s Infrared Telescope in Hawaii, the emerging picture of Edd-1 is consistent with a binary where at least one object is a massive star throwing off a thick stellar wind. If the other object is also a massive star, the X rays could arise where these winds collide.

But Edd-1’s infrared spectra don’t seem very similar to those of known massive-star binaries, with O-type or Wolf-Rayet stars. So, Mikles thinks the companion is a neutron star or a black hole. It’s difficult to distinguish between them, she explains, but, if she were betting on it: “I’d say it’s a black hole.”

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