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Space Science

Milky Way's Black Hole Wasn't Always Such a Wimp 83

Posted by Soulskill
from the you-wouldn't-like-me-when-i'm-angry dept.
scibri writes "Sagittarius A*, the dormant supermassive black hole that lies at the center of our galaxy, was much more active not that long ago. Astronomers using the Fermi Gamma-ray Space Telescope have picked up some faint gamma-ray signals that suggest Sagittarius A* was emitting a pair of powerful gamma-ray jets like other galactic black holes as recently as 20,000 years ago (arXiv paper). If our black hole was more active in the past, it could explain why Sagittarius A* seems to be growing about 1,000 times too slowly for it to have reached its current mass of about four million solar masses since the Galaxy formed about 13.2 billion years ago."
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Milky Way's Black Hole Wasn't Always Such a Wimp

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  • dormant black hole? (Score:5, Interesting)

    by ZombieBraintrust (1685608) on Wednesday May 30, 2012 @04:38PM (#40160063)
    What makes a black hole dormant? Lack of gamma ray jets... ?
    • by Tanman (90298)

      I guess the hulk moved on to make movies instead of crushing solar systems . . .

      • If two black holes happens to be near each others, will they collide?

        Or will one of the black hole swallow the other?

        Will the bigger black hole swallowing up the smaller one, or will it be the reverse, the little guy biting chunks out of its bigger counterpart?

        And when two black holes interact with each others, what will happen to the dimensions?

        Will it create enough disruptions to the dimensions in the vicinity that temporary additional dimensions pop up here and there?

        • They Merge (Score:2, Interesting)

          by Anonymous Coward

          From the view of an outside observer, the larger (greater mass) black hole will appear to draw the smaller one in. In reality, they're drawn to each other, and eventually merge, like two drops of water meeting on a window pane. The singularities become one. Simulations suggest that the merger will radiate massive quantities of energy in the form of gravity waves, a major ringing of the bell.

          The ringing quickly dies down, and the only evidence of the merger being 1) the changed direction of movement relative

    • Re: (Score:3, Funny)

      by Anonymous Coward

      it's only dormant because Chuck Norris told it to relax

    • by buchner.johannes (1139593) on Wednesday May 30, 2012 @04:48PM (#40160235) Homepage Journal

      What makes a black hole dormant? Lack of gamma ray jets... ?

      Lack of gas and dust streaming in. The disk + torus the infalling gas produces while accreting produces all the radiation we see from black holes in active galactic nuclei (AGN). Another side effect are the jets that you can see in radio frequencies (although not in all AGN.

      There is actually a gas cloud falling in in these decades, so we might see our black hole light up. http://www.nature.com/nature/journal/v481/n7379/abs/nature10652.html [nature.com]

      • by cpu6502 (1960974)

        I'd like to know where this black hole came from. Was there some random star floating through space, which died, and then it started gobbling up everything? Including our galaxy (which will eventually fall in). Or maybe the superblackhole was a previous galaxy from ~25 billion years ago that fell into itself?

        I'll go ask the Vorlon.
        He's probably old enough to remember.

  • by Scarletdown (886459) on Wednesday May 30, 2012 @04:39PM (#40160071) Journal

    Just more evidence that eating turkey makes you sleepy. It would appear that our galaxy's super massive black hole ate too much space turkey, and now it is having a nice long nap.

    • by Zocalo (252965)
      Maybe it's just contemplating the celstial equivalent of a wafer thin after-dinner mint.

      I'd imagine the after effects might be a little more colourful than with Mr. Creosote though...
  • so at 4 million solar masses how much would a teaspoon of that stuff weigh?
    • by fuzzyfuzzyfungus (1223518) on Wednesday May 30, 2012 @04:42PM (#40160147) Journal
      I get the impression that concepts like 'volume' start to get a little tricky once you pass the event horizon...
    • by Colonel Korn (1258968) on Wednesday May 30, 2012 @04:49PM (#40160257)

      The singularity itself? A teaspoon of singularities would have infinite weight. Maybe you mean everything inside the event horizon? In that case calculate the Schwarzschild radius (2Gm/c^2) of 4 million solar masses, then get the density [4 million solar masses /(4/3 pi r^3)] and multiply by the volume of a teaspoon. I think the density of everything inside the event horizon for that big of a black hole is actually pretty low.

      • Re: (Score:2, Informative)

        by sanosuke001 (640243)
        4x10^6 solar masses = 7.95568 × 10^36 kilograms
        Schwarzchild radius = 1.1804758431349163 x 10^10 meters
        4/3 pi r^3 = 6.89064573 × 10^30 m3


        mass / volume = 1.19612658 × 10^-27 kg / m3
        1 tsp = 5.0 × 10^-6 m3
        1 tsp of Sagittarius A* = 5.9806329 × 10-33 kg
      • by Thiez (1281866)

        > The singularity itself? A teaspoon of singularities would have infinite weight.

        No, it wouldn't. Black holes have a finite weight.

        • Re: (Score:3, Insightful)

          by Anonymous Coward

          > The singularity itself? A teaspoon of singularities would have infinite weight.

          No, it wouldn't. Black holes have a finite weight.

          Singularities consume no space, so you can fit an infinite number of finite weight singularities in a teaspoon. Hence infinite weight

          • > The singularity itself? A teaspoon of singularities would have infinite weight.

            No, it wouldn't. Black holes have a finite weight.

            Singularities consume no space, so you can fit an infinite number of finite weight singularities in a teaspoon. Hence infinite weight

            The mass is finite. The volume is 0. D=M/V. The density is infinite.

        • Re: (Score:3, Informative)

          by osu-neko (2604)

          > The singularity itself? A teaspoon of singularities would have infinite weight.

          No, it wouldn't. Black holes have a finite weight.

          Right, but an infinite number of singularities will fit in a teaspoon (or any volume, for that matter).

          • by Anonymous Coward

            You've touched on one of astrophysics' proverbial elephants in the room.

            There is no physics-based reason to believe there is a "singularity" at the center of a black hole, only a place where the math breaks down to a division-by-zero. In reality, some physical constraint would prevent further collapse, in the same way that degeneracy pressure halts the collapse of less massive stars.

    • by Anonymous Coward on Wednesday May 30, 2012 @05:00PM (#40160367)

      Don't know, none of our "teaspoon on a rope" measuring devices have been successfully pulled back out past the event horizon.

      On an unrelated note, we need more interns.

    • by Tarlus (1000874)

      so at 4 million solar masses how much would a teaspoon of that stuff weigh?

      That depends on how much the teaspoon itself weighs. =)

  • Asterisk (Score:4, Funny)

    by Megane (129182) on Wednesday May 30, 2012 @05:00PM (#40160373) Homepage
    It wasn't always such a wimp, but then it got caught doing steroids, so it had to have an asterisk after its name.
  • I dare you (Score:5, Funny)

    by Anonymous Coward on Wednesday May 30, 2012 @05:06PM (#40160413)

    Oh sure, it's easy to call it a wimp from way out here on the outskirts of the galaxy. But I bet you wouldn't call it a wimp if it were right in your face!

    • by rubycodez (864176)

      Chuck Norris got in its face. He told it to quit sucking so much, or he'd tear it a new asshole, reach inside, grab its singularity and turn it inside out. That's why we now have a quiet black hole in our galaxy.

  • Is anyone else disturbed that such an incredibly major change happened only 20,000 years ago?

    This could be worse than an ice age.

    • by osu-neko (2604) on Wednesday May 30, 2012 @05:52PM (#40160947)

      Is anyone else disturbed that such an incredibly major change happened only 20,000 years ago?

      This could be worse than an ice age.

      No. If, 20,000 years ago, it was much more active, it proves living in a galaxy with an active nucleus is not a problem. What it means is, if it becomes more active again, we don't really have anything to worry about -- we've been living with the "problem" for most of five billion years and gotten along just fine...

      • by Kaenneth (82978)

        Unless there is some unknown thing about the radiation stopping that allowed civilization to develop.
        Like a lower rate of mutations allowing humanity to become genetically stable.
        Sounds like a good Sci-Fi premise.

    • Re: (Score:3, Funny)

      by SJHillman (1966756)

      Al Gore went back in time 20,000 years (and you thought he only invented the Internet) to begin the process of Galactic Cooling so counteract the effects of Global Warming.

    • http://www.google.com/search?q=galactic+superwave+theory [google.com]

      One example:
      http://www.etheric.com/LaViolette/Predict.html [etheric.com]
      "Subsequent concurrence (1998): In 1988, when presented with Dr. LaViolette's Galactic explosion hypothesis, astronomer Mark Morris dismissed the idea as having no merit. However, in 1998 after ten years of observation, Morris was quoted as saying that the center of our Galaxy explodes about every 10,000 years with these events each lasting 100 years or so."

      Imagine if you were to go outside one

  • quieted by mass (Score:5, Interesting)

    by Shavano (2541114) on Wednesday May 30, 2012 @08:15PM (#40162321)
    It was explained in my astrophysics class that when a black hole reaches a certain mass that whole stars pass inside the event horizon before being torn up by tidal force. Then the singularity no longer has a big accretion disk and the radiation emitted by infalling matter is trapped within the event horizon. So it goes quiet.
    • It was explained in my astrophysics class that when a black hole reaches a certain mass that whole stars pass inside the event horizon before being torn up by tidal force.

      Then the singularity no longer has a big accretion disk and the radiation emitted by infalling matter is trapped within the event horizon.

      So it goes quiet.

      Who was your lecturer? Pick a mass, any reasonable mass for a black hole, and calculate it's Schwarzschild radius. Now add the diameter of a star, any star, to that radius and calculate the gravity field at that distance from the center of the black hole. Do you notice the difference? That tidal force will tear any star apart. It will tear iron apart.

      Furthermore, it is very unreasonable to assume that the only object orbiting the black hole is the single ingested star. Most (all?) black holes have large qua

      • Just a followup: let us assume the largest black hole that we can imagine, ingesting the smallest star that we can imagine, in the interest of minimising the tidal forces on the star. In this extreme hypothetical case of no tidal force on the star until it contacts the event horizon, you will agree that the star will have also drag down with it minimal material from the accretion disk, and certainly not all of it. Now imagine what a star passing through the remaining material does to the distribution of tha

        • by Shavano (2541114)
          That depends on what you mean by quiet. A star getting ripped apart by a smaller black hole would emit more radiation.
      • Re: (Score:2, Informative)

        by Anonymous Coward

        The Schwarzchild radius is proportional to the mass M. The tidal effect is proportional to the derivative of the gravitational field, which is proportional to M / R^3. Setting R to be the Schwarzchild radius, to measure the tidal effect at this point, we find that it is proportional to 1 / M^2. So the more massive a black hole is, the smaller the tidal effect at its event horizon - and for a sufficient black hole mass, the tidal effect must be insufficient to break up a star.

        Calculating the mass at which

        • The Schwarzchild radius is proportional to the mass M. The tidal effect is proportional to the derivative of the gravitational field, which is proportional to M / R^3. Setting R to be the Schwarzchild radius, to measure the tidal effect at this point, we find that it is proportional to 1 / M^2. So the more massive a black hole is, the smaller the tidal effect at its event horizon - and for a sufficient black hole mass, the tidal effect must be insufficient to break up a star.

          Calculating the mass at which this happens is left as an exercise for the reader. ;-)

          Thanks. I address this in my followup post, posted as a reply to self. And I also left the "insufficient tidal effect" BH mass as an exercise for the reader, for any arbitrary definition of insufficient!

      • by Shavano (2541114)
        For a star the size of the sun, at 90 million solar masses, a star like the sun would stay intact as it fell through the event horizon. \
      • by Shavano (2541114)
        The most massive black holes ever observed are over a billion solar masses. At 90 million solar masses, the sun could hold together at least with respect to gravity vs. tidal force. If you were observing this happen, you would see the sun getting dimmer and redder as it fell toward the event horizon, and at some point I think it would just go dark. You wouldn't see a flash or flare because a big piece of matter just disappeared from the observable universe without making a splash.
        • You are correct, the post that you replied to did not account for galaxy-core supermassive black holes. However, the followup post (rely to self) addresses this.

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