New observations show black holes spew out way more than they eat

November 20, 2023   Issue #646

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Shameless Self-Promotion

Where I’ll be doing things you can watch and listen to or read about

Did you know I wrote a book? And that it’s really good?

Well, I thought so. And so did the Financial Times, which put Under Alien Skies on its list of best science books of 2023! Whoa. They call it, “…a vivid guidebook for space tourists in the distant future.” Cooool.

Also, I did an interview about it with Kerri Miller of Minnesota Public Radio, and that’s now online.

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

Black holes are sloppy eaters. It’s a common misconception that anything that gets too close to them inexorably falls in — in reality, stuff gets shredded long before it gets too close, and that material will then form a flattened disk called an accretion disk which heats up hugely due to friction. In the case of big gas clouds or shredded stars, for example, the material gets superheated and carries a strong magnetic field. As it spirals in, the magnetic fields wind up like tornadoes, and material is swept up and shot out in twin beams at phenomenally high speeds. It can get so bright that an actively feeding supermassive black hole in the center of a galaxy can outshine all the starlight in the galaxy combined! We call these active galaxies.

But how much material falls in versus what’s spat out? That’s hard to measure because these black holes are in the centers of other galaxies, millions of light-years away, so seeing them on the scales needed — just a few light years — is incredibly difficult.

However, new observations appear to have done just that. Using the wonderful ALMA observatory, astronomers took extremely high-resolution images of the center of the Circinus galaxy about 13 million light-years from Earth. It’s a well known active galaxy, so they used ALMA to trace the motion of gas in different phases — molecular (meaning cool), atomic (warmer), and ionized plasma (very hot). They were able, for the first time, to trace the dense molecular gas down to sub-parsec scales (a parsec is 3.26 light-years).

What they found is that only about 3% of the material falls into the black hole itself, causing it to slowly grow [link to research paper]. The rest is blasted outwards in what’s called galactic feedback; it goes back out into the galaxy. Some of that may once again fall toward the black hole, but a lot of it slams into gas and dust between stars, compressing clouds and triggering star formation. In some cases that material may leave the galaxy completely as well, lost to intergalactic space.

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In the image above, you can see dense carbon monoxide (very common in galaxies) marking the spiral arms, with other gases indicated in the image caption. What’s shown in green is hot hydrogen cyanide gas (also common, it has the simple chemical formula of HCN) and that traces the accretion disk around the black hole. You can see a beam of hydrogen gas (astronomers call this a jet) right at the center, and as expected it’s perpendicular to the disk; the two jets shoot away “up and down” from the disk due to the magnetic acceleration. The one on the opposite side isn’t seen; that may be due partly to stuff in between us and it blocking its light, or an effect called relativistic beaming, where stuff moving near the speed of light has its light focused into a beam in the direction of travel. Since it’s moving away from us, the light is focused away from us.

Anyway, this is very cool! We know that if too much material gets too hot near the black hole, essentially all that matter gets blown away by the intense radiation generated — this is called the Eddington Limit. But if the matter is cooler some of that material can fall into the black hole, and these new observations puts some numbers on that ratio, providing empirical constraints for the first time. It’s an important result, and I hope we see more observations like it soon.

News Roundup

Who can keep up with everything these days?

• As you’ve probably heard, SpaceX had a second Starship flight test that ended with both the first stage booster and the upper Starship stage exploding (probably auto-detonated via on-board software that detected anomalies). A lot of folks (mostly not familiar with how spaceflight actually works) are calling this another failure, but I think that’s very premature if not outright unfair; the stages separated and the upper stage got into space, two critical steps that did not happen in the first flight. No one expected a flawless flight, and these tests are incremental in nature, with a lot of engineering issues found that can be fixed for the next test. Remember that Falcon 9 did not do well for its first few flights, and it’s now the most successful rocket ever flown. And yes, I know, Elon. Y’all know how I feel about him. I don’t think the company can do much about distancing themselves from his horrid and frankly despicable ideologies. This must be an incredibly difficult situation for NASA (and other agencies; read this OpEd calling Musk a national security risk), and I can imagine more than a few folks there are dealing with acid reflux right now. I have no idea how this will pan out, and at the moment I’m not in a position to predict it.

• On Friday and Saturday, November 17/18, Mars was on the other side of the Sun from Earth. Literally; the Sun directly blocked our view of the Red Planet. Most planets don’t orbit the Sun in the exact same plane as Earth, so they wind up missing it by a little bit from our point of view in the sky. But in this case, Mars was physically blocked by the Sun. That means our robots on and around the planet can’t talk to us, so they pause in their missions. Many get commands sent to them that can keep them operating while we’re out of contact, including some NASA mission that will continue to take data that they’ll upload back to us later.  In general this happens for about a month when Mars gets too close to the Sun in the sky, and radio signals get garbled as they pass through the solar corona; in this case it’ll be far enough away from the Sun again in December. Due to both the motions of Mars and Earth, this solar conjunction happens every 25 to 26 months, so it’ll be around January 2026 until it happens again.

• Via Orbital Index I learned there’s a site that allows you to look for hotels where the skies are dark! It combines a light pollution map with an online booking listing to present an interactive map. Clever. I noticed it gets darker where I live now than I was used to in Colorado, and found I’m around a Bortle 3 location, maybe a touch brighter. I need to get my ‘scope out!

Et alia

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!