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, February 29, 2020

The second biggest bang

There are times in science where -- if you're going to describe something accurately -- you rapidly become lost in superlatives.

That was my reaction to a paper this week in Astrophysical Journal titled, "Discovery of a Giant Radio Fossil in the Ophiuchus Galaxy Cluster," by a team led by Simona Giacintucci of the Naval Research Laboratory.  Here's what the researchers had to say about it:
The Ophiuchus galaxy cluster exhibits a curious concave gas density discontinuity at the edge of its cool core...  Using low-frequency (72-240 MHz) radio data from MWA GLEAM and GMRT, we found that the X-ray structure is, in fact, a giant cavity in the X-ray gas filled with diffuse radio emission with an extraordinarily steep radio spectrum.  It thus appears to be a very aged fossil of the most powerful AGN [active galactic nucleus] outburst seen in any galaxy cluster (pV∼5×10^61 erg for this cavity).  There is no apparent diametrically opposite counterpart either in X-ray or in the radio.  It may have aged out of the observable radio band because of the cluster asymmetry.  At present, the central AGN exhibits only a weak radio source, so it should have been much more powerful in the past to have produced such a bubble.  The AGN is currently starved of accreting cool gas because the gas density peak is displaced by core sloshing.  The sloshing itself could have been set off by this extraordinary explosion if it had occurred in an asymmetric gas core.  This dinosaur may be an early example of a new class of sources to be uncovered by low-frequency surveys of galaxy clusters.
To say that this explosion was huge doesn't even begin to describe it.  The energy output of this outburst puts it in second place ever -- the only event we know of that was more energetic than this was the Big Bang itself.

Its size isn't the only odd thing about it.  "We've seen outbursts in the centers of galaxies before but this one is really, really massive," said Melanie Johnston-Hollitt of Curtin University's International Centre for Radio Astronomy Research, in an interview at Phys.Org.  "And we don't know why it's so big.  But it happened very slowly—like an explosion in slow motion that took place over hundreds of millions of years."

However slow it was, the explosion blew a hole in the sphere of superhot plasma surrounding the massive black hole at the center of the galaxy.  Study lead author Simona Giacintucci compares it to the pressure from the eruption of Mount Saint Helens blowing off the entire top of the mountain, leaving a crater behind.  "The difference," she said, "is that you could fit fifteen Milky Way galaxies in a row into the crater this eruption punched into the cluster's hot gas."

[Image licensed under the Creative Commons Rogelio Bernal Andreo, Rho Ophiuchus Widefield, CC BY-SA 3.0]

Johnston-Hollitt, who directs the Murchison Widefield Array in Western Australia, said that despite the enormity of the relic explosion, it was only recently observed because of a drastic improvement in astronomers' ability to observe the skies in the very-low-frequency end of the spectrum.  "It's a bit like archaeology," she said.  "We've been given the tools to dig deeper with low frequency radio telescopes so we should be able to find more outbursts like this now."

So there might be other colossal explosion remnants out there just waiting to be found.

What it brings up for me, non-researcher that I am, is to wonder what on earth could have caused a detonation on this scale.  To my knowledge, the explanation is still uncertain, and in fact can't be accounted for by any known natural process.  The lack of a mechanism and the size of the outburst led scientists at first to doubt the measurements were correct.  "People were skeptical because of the size of outburst," Johnston-Hollitt said.  "But it really is that."

And improvements to the Murchison Widefield Array is improving its sensitivity by a factor of ten, which means we're only seeing the beginning of discoveries like this, and who knows what else.  "The Universe is a weird place," Johnston-Hollitt said.

Indeed it is.  Awe-inspiring to the point of bowling over your brain, at times.  Look around you at your house, town, and region, your friends, family, and pets, even the bigger concerns of politics and global conflict -- and realize that on the grand scheme of things, we are minuscule, hardly even a blip on the surface of cosmic space-time.  Humbling and a little scary, isn't it?

But the human brain isn't built to conceptualize such enormities, and it's best not to dwell on it.  On the whole, it's probably better to have another cup of coffee and think about something else for a while.


One of my favorite people is the indefatigable British science historian James Burke.  First gaining fame from his immensely entertaining book and television series Connections, in which he showed the links between various historical events that (seen as a whole) play out like a centuries-long game of telephone, he went on to wow his fans with The Day the Universe Changed and a terrifyingly prescient analysis of where global climate change was headed, filmed in 1989, called After the Warming.

One of my favorites of his is the brilliant book The Pinball Effect.  It's dedicated to the role of chaos in scientific discovery, and shows the interconnections between twenty different threads of inquiry.  He's posted page-number links at various points in his book that you can jump to, where the different threads cross -- so if you like, you can read this as a scientific Choose Your Own Adventure, leaping from one point in the web to another, in the process truly gaining a sense of how interconnected and complex the history of science has been.

However you choose to approach it -- in a straight line, or following a pinball course through the book -- it's a fantastic read.  So pick up a copy of this week's Skeptophilia book of the week.  You won't be able to put it down.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

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