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

Status: OK

[Sneeka2]

V200 Cygni

There, FTFY.

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:Watch a movie of V404 Cyg in the optical

[StupendousMan]

My apologies. I should have marked the position of the variable star. I've just modified the web page so that the initial picture indicates the target -- click on that initial picture to see the movie. Thanks for pointing that out.

since you're doing such extensive image processing anyway, why not correct for the blooming of bright stars and make them all the same size and shape?

Well, in part, because I'm an astronomer, not a cinematographer, so my ability to make nice movies is rather limited. I could claim that there's some pedagogical value in seeing the ugly nature of the real scientific images, but, actually, that would just be covering up for the fact that I'm lazy.

Re:Watch a movie of V404 Cyg in the optical

[funwithBSD]

Error: V404 Not Found

The real importance of the event

[m.alessandrini]

IANAA, but I think the exceptional thing here is that such a huge change in an astronomical object can be seen in an human-life time scale, instead of millions years as usual.

Re:The real importance of the event

[CBM]

Well yes and no. There are probably hundreds of thousands of these systems, lying dormant, in our galaxy. Each one is probably fed by a nearby orbiting donor star, that transfers matter in a slow trickle to an accretion disk which surrounds the black hole. The material kind of stays there, dormant, in the disk. When enough density builds up in the accretion disk, there is an hydrodynamic instability that causes flow to suddenly turn on. This will flush out the disk, the system will eventually turn off after a few months, and then it will lie dormant again. The time scale for recurrence could be a year, it could be thousands of years; it kind of depends on the mass transfer rate from the donor star and the mass of the black hole. There are typically tens of black hole outbursts per year in our galaxy, but V404 Cyg is one of the brightest known.

Sloppy language

[argStyopa]

Even in TFA, using the term 'reawakened' is so totally mischaracterizing the situation.

It's not like black holes go dormant, or gravity goes to sleep. No, clearly it's been short of significant infall material and has suddenly consumed something substantial, leading to a burst of outflow energy.

It's interesting and fascinating, but really we can do better to inform the general public (who is already woefully scientifically ignorant) than using tabloid-level language to explain it.

Obligatory relevant xkcd: https://xkcd.com/1133/ 'Up goer five'

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."

Old news

[Anonymous Coward]

Pfft ... this happened 7800 years ago ... go /.

Re:Well, not exactly current events

[Hognoxious]

By slashdot's standards that's good. It can take almost as long for events happening on the other side of the Earth.