Black holes and white slopes

By Daniel Holz | February 25, 2010 9:23 pm

I spent last week attending the “Formation and Evolution of Black Holes” conference at the Aspen Center for Physics, organized by Andrea Ghez, Vicky Kalogera, Fred Rasio, and Steinn Sigurdsson (who blogs over at the Dynamics of Cats). It was a great mix of observers and theorists, and we covered the full range, from stellar-mass black holes in our galaxy to supermassive black holes on the far side of the Universe. I was particularly interested in two topics: gravitational-wave recoil and black hole binary inspiral (I’ll blog about both soon enough). And I made another pilgrimage to the Highlands bowl, this time with 15″ of virgin powder.

The Aspen Center runs a public lecture series in conjunction with each conference. So last Wednesday Andrea Ghez gave a lecture on the black hole at the center of our galaxy. It’s our closest big black hole, roughly 25,000 light years (2×1017 kilometers) away, and four million times the mass of our Sun. Andrea has been leading a team studying the motion of stars orbiting around this black hole. These orbits are one of the best ways (short of the detection of gravitational waves from black hole mergers) of confirming that black holes exist. The orbits tell us the mass of the central object. And the innermost passage of the closest orbit gives us an upper limit on the size of the central object. Combining these numbers gives us a lower limit to the density of the “dark object” at the center of our galaxy. At this point, a black hole is the only viable model for what we see. There is no way to make sense of the orbits using a cluster of (dark) stars at the center, or a massive gas cloud, or anything else we can think of. Gravity tells us that any normal stuff we put there (including “conventional” dark matter) will evaporate or collapse to a black hole. We are not yet probing the horizon of the black hole (in some sense, its surface), but we are getting closer and closer with each passing year.

But, more importantly, Andrea is responsible for one of the coolest movies in all of science:

This shows the orbits of stars around our galactic center. This isn’t an artist’s conception. This isn’t some abstraction of other data. This is a real movie of stars circling the black hole over the last 15 years. In particular, watch S-02. It loops around the black hole, and closes its orbit; we have watched it over one full S-02 “year”. It is an incredible feat of observational astronomy to make these movies. It requires adaptive optics on the largest telescopes in the world (the Keck telescopes on Mauna Kea). We used to think of the heavens as eternal and unchanging. Now we watch movies of stars orbiting black holes.

  • James

    That is an amazing movie.

    It’s quite interesting to think of stars that orbit the galactic center more often than some of the planets orbit our own star :)

  • Lab Lemming

    How does one powder a virgin?

  • chris

    wow, this is an impressive movie indeed! it’s absolutely amazing what modern telescopes can do.

  • arcanum

    Looks like a soliton to me!

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  • Low Math, Meekly Interacting

    OK. Now I know this is a lot to ask, but how different must the sky be orbiting one of these stars? Just think what it would be like to be (a very durable) astronomer on a planet orbiting a star in the vicinity of Sagittarius A*. What a lot to keep track of!

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  • Richard Drumm The Astronomy Bum

    I’d LOVE to have an .mpg of this to include in my astronomy talks…
    Got a link to a downloadable file?

  • daniel

    Richard, there are many images/movies available off of Andrea Ghez’s homepage. The movie I show above is available here.

  • jackd

    S-02 and S-16 made my jaw drop. How fast is S-16 moving at closest approach?

  • Xerxes

    According to the webpage, S0-16 gets within 45AU and achieves 4% of light-speed.

  • Austin Frisch

    It looks like the s-16 orbit is going to close as well. Anyone know how many orbits before we’d see visible precession?

  • Mandeep

    Dan- way cool, but you didn’t mention one thing (alluded to above) that to me is the absolute coolest about this whole deal — that the stars actually have different periods in the 3 spherical coordinates, because of GR effects, and this makes the orbits not close. and i believe we have already seen these effects in the orbits that Andrea has been tracking. to me, seeing GR effects in such an obvious way is just highly cool (yes, of course, this is only an extreme version of what Mercury feels, but just obvious to the eye).

    [Further, i once saw Scott Hughes give a talk that in the relatively near future said we would be able to directly see the asymmetry (due to rotation) of the galactic center black hole directly once we get to microarcsecond interferometry, something along these lines.. that is even *cooler*.. :-> ]

  • Samuel A. (Sam) Cox

    Xerxes link in #11 is well worth reading…particularly the last paragraph.

    It is pretty clear that the singular condition…macrosocpic (Black Holes) or sub-microscopic (The Planck Realm) as observed from our frame of reference is foundational to understanding our particulate existence. So are the GR time dilation formulae, which relate to the way a “manifold” (space) is observed to exist from our frame of reference.

    An AWESOME post!…with great links. I was last up at Keck in 06 and got a light case of altitude sickness, but the trip up, and tour of the facility were well worth my time. It’s an awesome site too, Holy to the local people. There were still snow drifts up there in late March…the students at the university told me the snow came early this year…

  • eric gisse

    FUCCCCKKKKKKKKKKKKKKK, I HATE asshole webforms that bitch that you need to put in an email then delete what you wrote. FUCK.

    Let’s try this again.

    * The movie Ghez did is a followup to an animated GIF that’s been going around for years. Still cool.

    * Gillessen has done work complementary to Ghez, and has established that pericenter precession due to Schwarzschild is not currently observable. I’ve asked Ghez about this previously to reading Gillessen, and she said that it should be possible in the next decade or so.

    Pericenter advance for the star S-2 should be 0.18 degrees per orbit (Gillessen), which will be cool as hell to see.

    S. Gillessen,, “Monitoring stellar orbits around the massive black hole in the galactic center”, ApJ 692 p 1075

    * Doeleman and crew have used VLBI imagery to directly observe Sgr A*, which Gillessen has shown is within 2mas of the black hole proper.

    “Event horizon-scale structure in the supermassive black hole candidate at the galactic center”, S. Doeleman, et. al. , Nature 455, Sept 4 2008 p78

  • Richard Drumm The Astronomy Bum

    Thanks, Daniel! I will incorporate one of these files into my PowerPoint “What is Astronomy?” ASAP. I talked to Cub Scouts at McCormick Observatory last night and actually talked about this very thing, how we can’t see a BH but can see its gravitational effects. Now I’m really ready to answer that kid’s question… Next time fer sher!
    Thanks again!

  • spyder
  • Just Learning
  • Roman

    From my layman point of view this is still the most astonishing, real time astronomical observation I’ve seen. There is really a difference between some photoshoped “artist impressions”, even good ones, and something like this.
    So what are the latest theories of how those crazy stars formed?

  • Tim

    Suppose one of these close approach orbits goes behind the black hole from our perspective. Would we then be able to observe gravitational lensing and maybe even a “jump” from one side to the other?

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  • Tomas

    What happpened to the movie?

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  • Jon Hanford

    Most ‘EU/PU specialists’ insist the 3.6 million solar mass is in a ‘faint’ period while the ‘anomalous’ plasma stars far outshine the massive celestial object. Recent ESO observations have established a permanent flicker of Sgr A* at NIR and radio wavelengths. PU is totally misguided.

  • Trond Engen

    So black holes are bigger the farther back in time we see? Does this mean that even big black holes decay or that they at some point burst?

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