Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Saturday, January 20, 2024

The empty galaxy

A couple of weeks ago, I began a post with a quote from physicist Albert Michelson in which he confidently claimed that everything in physics was pretty well settled -- in 1894.  Right before the discovery of the relativity and quantum mechanics would shake science to its foundations.

I read yet another paper just yesterday highlighting the inadvertent irony of Michelson's statement, and which once again shows us that we are very far from understanding everything there is to understand.  This one was about the accidental discovery of a galaxy that has an extremely odd characteristic.

It appears to have no stars whatsoever.

The object, dubbed J0613+52, is about ten times less massive than the Milky Way -- so smaller than your typical galaxy, but still pretty damn huge, weighing in at about two billion solar masses.  But the entire thing is made up of diffuse gas and dust -- no stars at all.

Because of this, it has an extremely low luminosity.  It was only discovered because of a mistake -- the astronomers at the Green Bank Observatory were trying to aim it elsewhere, but had mistyped the coordinates -- but when the telescope focused on the spot, they saw a blip of hydrogen spectral emission lines in what appeared to be an empty region of space.  More detailed study of the spot found that the emission lines were coming from a huge but faint dust cloud that was on the scale of galaxies mass-wise but seemed to have undergone no star formation.

"It’s likely there is a decent amount of dark matter present as well," said Karen O’Neil, senior scientist at Green Bank, who led the research.  "But lingering uncertainties about the dark galaxy’s exact physical size make associated dark-matter estimates hazy at best...  J0613+52 is completely isolated, with no neighboring galaxy closer than 330 million light-years or so; our own Milky Way, in fact, appears to be the object’s closest-known companion.  In these void areas of the universe, gas should be too diffuse to form any galaxy-like object.  Clearly that’s not quite true."

Robert Minchin, of the National Radio Astronomy Observatory in New Mexico, heard O'Neil present the findings at last week's meeting of the American Astronomy Society, and was obviously impressed.  "I think it’s definitely a real detection," Minchin said.  "It does look like a primordial object.  It’s a bit like discovering a living dinosaur and having it there to study."

Artist's depiction of J0163+52 [Image credit: STScI POSS-II (starfield); additional illustration by NSF/GBO/P.Vosteen]

What puzzles me is that J0613+52 is only ("only") 330 million light years away, so not even close to being the farthest galaxy we've seen.  The universe as a whole is forty times older than the light we're seeing from this bizarre empty galaxy, so you'd think it'd have had plenty of time to form stars from all that hydrogen gas.  Instead, it seems to be a relatively homogeneous dust cloud.  You have to wonder, what's keeping it that way?  Gravity is relentless and inexorable -- the current models indicate that even tiny anisotropies (unevenness) in the mass distribution will result in the denser regions gaining mass at the expense of the less dense regions, resulting in clumps of matter that eventually coalesce into stars.

For a dust cloud that massive to last over twelve billion years without forming stars is somewhere beyond peculiar.

It may be that I'm missing something, here.  (Okay, given that I'm not an astrophysicist, it's certain that I'm missing something.)  But even with my no-more-than-basic understanding of astronomy, this object seems really peculiar.

As is the fact that it was discovered accidentally because one of the astronomers had entered a typo in the coordinates.

I'm sure the astronomers are going to be busy looking at the empty galaxy and trying to figure out what it is, and also looking for others.  Given its extremely low luminosity, and the fact that we found it by basically aiming a big telescope at a random spot in the sky, you have to wonder how many other similar structures there are.

I'll end with the words spoken by Hamlet, which have been quoted many times before but seem apposite: "There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy."


No comments:

Post a Comment