Black Hole Awakens After 26 Years

schwit1 writes: For the first time since 1989, the black hole in V404 Cygni, a system comprising a black hole and a star, has reawakened, suddenly emitting high energy outbursts beginning on June 15. The outbursts are probably occurring because the black hole is gobbling up material that has fallen into it. While the 1989 outburst helped astronomers gain their first understand of the behavior of a black hole in a star system, this outburst will help them understand how such systems evolve and change over time. The European Space Agency (ESA) reports: "First signs of renewed activity in V404 Cygni were spotted by the Burst Alert Telescope on NASA's Swift satellite, detecting a sudden burst of gamma rays, and then triggering observations with its X-ray telescope. Soon after, MAXI (Monitor of All-sky X-ray Image), part of the Japanese Experiment Module on the International Space Station, observed an X-ray flare from the same patch of the sky. These first detections triggered a massive campaign of observations from ground-based telescopes and from space-based observatories, to monitor V404 Cygni at many different wavelengths across the electromagnetic spectrum."

Comments

I hate the term "awakens"

[jfdavis668]

The black hole just sat there. Something else collided with it, and the black hole gravity pulled it in. The something, probably a gas cloud, heated up during the fall and started to emit radiation. How does this cause something to wake up?

Re:I hate the term "awakens"

[Psychotria]

The something, probably a gas cloud [...] How does this cause something to wake up?

I dunno about you, but if someone farted in my face while I was sleeping I'd probably wake up as well.

Re:I hate the term "awakens"

[CBM]

Actually the term is appropriate. Gravity doesn't disappear, but material can orbit the black hole in an accretion disk, in a dormant state. When enough material builds up in the disk, accretion flow to the black hole can activate. It's called an accretion disk instability. In the astronomy business we would say the black hole has become active, or is having a transient outburst, but awaken is fine for public consumption.

being an old hand on slashdot

[nimbius]

Im pleasantly surprised the words 'black hole awakens after 26 years' isn't followed up with some sort of infuriating article on SCO.

Re:being an old hand on slashdot

[Sneeka2]

No worries, that's a different kind of 'hole.

Watch a movie of V404 Cyg in the optical

[StupendousMan]

I've been using our university's observatory to take images of V404 Cyg for the past week. On Jun 23/24, the star underwent a particularly crazy series of variations: over a period of six hours, it fell to just 5 percent of its initial brightness, then recovered almost to its starting point.

I made an animated GIF showing the star's changes over this period. You can see it on my observing log for the the night:

http://spiff.rit.edu/richmond/...

That page also includes my full dataset, and pointers to additional reading.

The star is currently bright enough -- mag 11-14 -- to be studied easily with small telescopes. Anyone interested in joining the effort should start with the American Association of Variable Star Observers (AAVSO) -- go to their campaign page at

http://www.aavso.org/aavso-ale...

Re:Watch a movie of V404 Cyg in the optical

[StupendousMan]

Good idea. We astronomers try to eliminate such possibilities by measuring OTHER stars nearby and comparing their variations to those of the target. In this case, nearby stars didn't vary over the night, so we can rule out clouds in the Earth's atmosphere, which would have affected them all.

Now, it's possible that a cloud near the star itself could have something to do with this variation .... but the timescale for motions of such big objects is almost always far longer than a few hours. So, it's more likely that the variations are due to changes in the luminosity of the accretion disk around the black hole than to the motions of a big obscuring cloud in this case.

Re:Sloppy language

[CBM]

Actually, yes, black hole *systems* go dormant. The system consists of the black hole itself, but also an accretion disk orbiting the black hole, and also an orbiting donor star which is providing a relatively steady flow of matter to the outer part of the accretion disk.

Matter can stay there, in the accretion disk for a year, tens of years, or thousands of years, until enough mass density builds up. At that point, an accretion disk instability turns on and you get a transient outburst, and then it will take a few months to flush out the disk.

Google for "dwarf nova instability."