Biggest and brightest

If you're the kind of person who likes having your mind blown by superlatives, astrophysics is the science for you.

I ran into two really good examples of that last week.  In the first, a paper in the journal Monthly Notices of the Royal Astronomical Society, from research led by astrophysicist Ruth Daly of Pennsylvania State University, found that the massive black hole at the center of the Milky Way -- Sagittarius A* -- is spinning so fast it's actually warping the fabric of space time around it, flattening it into the shape of a football.

The "no-hair theorem" of the physics of black holes states that they are rather simple beasts.  They can be completely characterized using only three parameters: their mass, charge, and angular momentum.  The name comes from the quip by physicist John Archibald Wheeler that "black holes have no hair," by which he meant that there are no other adornments you need to describe to get a full picture of what they're doing.  However, I've always been puzzled by what exactly it means to say that a black hole has angular momentum; objects with mass and spin, such as a twirling top or the rotating Earth, have angular momentum, but since the mass in a black hole has (at least as far as we understand them) collapsed into a singularity, what exactly is spinning, and how could you tell?

Last week's paper at least answers the second half of the question.  Using data from x-ray and radio wave collimation and material outflow from Sagittarius A*, astrophysicists can determine how much spacetime is being deformed by the angular momentum of the black hole, and from that determine its rate of spin.

And it's spinning fast -- an estimated sixty percent of the maximum possible rate, which is set by the universal speed limit that matter can't travel at or faster than the speed of light.  The deformation is so great that the fabric of spacetime is compressed along the spin axis, so it appears spherical from above but flattened from the side.

[Image is in the Public Domain courtesy of NASA/JPL]

The second piece of research comes from a study at the European Southern Observatory, and was published in Nature Astronomy.  It looks at the recent discovery of the brightest object known, a quasar (an active galactic nucleus containing a supermassive black hole) that -- get ready for the superlatives -- is five hundred trillion times more luminous than the Sun, contains a black hole that has seventeen billion times the mass of the Sun, and is consuming one Sun's worth of mass a day.  This object, given the unassuming name of J0529-4351, is twelve billion light years away, making it also one of the most distant objects ever studied.

"All this light comes from a hot accretion disk that measures seven light-years in diameter -- this must be the largest accretion disk in the Universe," said study co-author Samuel Lai, of Australian National University.  If he sounds a little blown away by this -- well, so are we all.  A seven-light-year accretion disk means that if it were placed where the Sun is, not only would its accretion disk engulf the entire Solar System, it would extend outward past the five nearest stars -- the triple-star system of Alpha/Proxima Centauri, Barnard's Star, and Luhman 16.

I don't know about you, but something on that scale boggles my mind.

And that's not a bad thing, really.  I think we need to be reminded periodically that in the grand scheme of things, the problems we lose so much sleep over down here are pretty minuscule.  Also, it's good to have our brains overwhelmed by the grandeur of the universe we live in, to be able to look up into the night sky and think, "Wow.  How fortunate I am to be able to witness -- and in some small way, understand -- such wonders."

****************************************