Can Supernovae Switch Black Holes On And Off?

notcarlos writes: "There's an article at Space.com which discusses how a supernova can trigger a sudden burst of mass "consumption" in black holes. However, when the shock waves from that explosion dissapates, the black hole goes into "remission" and takes in less mass. Nifty, eh?"

Breathless-journalism alert!

[Max Hyre]

Switching black holes ON and OFF?! This must be some totally-new observation implying a massive change in our UNDERSTANDING of the laws of physics!

Well, no...they're really talking of switching it the same way you'd switch a cliff's lemming consumption off and on, by either fencing the creatures away from the cliff, or herding them toward it. Big deal---compared to the speculation engendered by the headline.

That said, it's still interesting on its own terms: a supernova can first blow massive amounts of matter toward the black hole, supplying it with above-average input. Then, after the shockwave has passed the hole, it drives matter away (by the same mechanism, pushing it ahead of the shock), lowering the amount available for the hole to suck in.

</grouch mode>

Engineering Problem

[SEWilco]

The engineering to make use of this is just a little beyond us. :-)

Moreover, they don't mention any observations that the black hole is evaporating during starvation. That would be interesting data.

Imagine...

[CptnHarlock]

... making a computer out of blackholes turned on and off by supernovas!.. or rather: Imagine e beowulf cluster of these!.. ;-)

--
"No se rinde el gallo rojo, sólo cuando ya está muerto."

Only Post

[Deanasc]

Only Post? (at least an hour after this came up) Wow. Seriously though I thought that matter on the outside of the event horizon was pretty safe. If there's no matter to fall directly in then the black hole doesn't eat.

Hard to observe the evaporation

[Caid Raspa]

This black hole is close to the centre of the Galaxy, so there's plenty of other radiating stuff around (the supernova leftovers mentioned in the article, lots of stars, insterstellar matter)

Also, they mention that this is a supermassive black hole, millions of solar masses. The Hawking radiation, or evaporation, is weaker for more massive black holes. The temperature of the event horizon of this black hole like this is propably much smaller than the 3 Kelvin cosmic background, so the evaporation can not be observed from earth. Perhaps a particle detector near the event horizon might be able to do it.

Re:Only Post

[jfrisby]

The event horizon is not the maximum extent of the black hole's gravitational field -- it's the point at which nothing can *escape* regardless of the amount of energy applied.

The distinction is that most matter isn't going to apply a lot of energy in an effort to escape -- it'll just fall in. A spaceship for example, would be pulled towards the black hole well beyond the event horizon, but before it reaches that point it could (theoretically) escape given sufficient energy. (although as you get close to the event horizon the energy required would quickly become phenominal...)

-JF