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The black hole at the center of the Milky Way is quiet now, but new evidence suggests that it woke up around 3.5 million years ago. And Enceladus may have the the building blocks of the building blocks of life.

Host: Caitlin Hofmeister

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Sources:
https://www.eurekalert.org/emb_releases/2019-10/acoe-nla100319.php
https://www.scienceinpublic.com.au/wp-content/uploads/ASTRO-3D-Ionisation-cones-full-paper.pdf
https://www.jpl.nasa.gov/news/news.php?release=2019-197
https://academic.oup.com/mnras/article/489/4/5231/5573821/
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Images:
https://commons.wikimedia.org/wiki/File:X-RayFlare-BlackHole-MilkyWay-20140105.jpg
https://www.eso.org/public/images/potw1511a/
https://images.nasa.gov/details-PIA12348
https://www.eurekalert.org/multimedia/pub/213073.php
https://www.istockphoto.com/photo/walton-lighthouse-at-the-santa-cruz-harbor-in-monterey-bay-gm1039589904-278298076
https://en.wikipedia.org/wiki/File:PIA17202_-_Approaching_Enceladus.jpg
https://www.jpl.nasa.gov/video/details.php?id=1404
https://www.istockphoto.com/vector/amino-acids-main-structural-chemical-formulas-gm474667562-65007551
https://www.nasa.gov/image-feature/jpl/pia20013/enceladus
https://www.nasa.gov/image-feature/jpl/pia21887/last-enceladus-plume-observation
https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA23173
https://www.istockphoto.com/photo/underwater-background-gm514419706-88089315
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(Intro)

Just like most major galaxies, our Milky Way's core is home to a supermassive black hole, and also like in most major galaxies, this black hole is currently quiescent, which is to say it's not actively eating a bunch of matter, but that doesn't mean it's always been that way.  Astronomers announced this week that they found more evidence that our black hole "woke up" around 3.5 million years ago, which is pretty recent in galactic terms, and it ate so much it belched out beams of radiation stretching over 200,000 light years into the void, an act of cosmic overindulgence that could tell us more about how galaxies change over time.

I should note here that these beams shot out of our galaxy perpendicular to the Milky Way's disc.  Our early human ancestors were already around at this point, but they wouldn't have been affected by or even have noticed this event.  Lucy was fine, guys.

It did affect the Magellanic stream, which is a long trail of gas coming up the large and small Magellanic clouds, the dwarf galaxies next door to the Milky Way, and we can still spot the side effects of this flare by looking at different kinds of light, both visible and not.  Previous research looking at x-rays, gamma rays, and the red part of the visible spectrum had hinted a massive explosion coming from the center of our galaxy anywhere from 2-8 million years ago, and this most recent finding adds ultraviolet observations collected by Hubble. 

By measuring the ratios of different carbon and silicon ions, the team concluded that regions of the Magellanic stream got caught in an ancient blast cone of ionizing radiation originating from the Milky Way's supermassive black hole, Sagittarius A*.  According to their models, this event dates back to 3.5 million years ago, which fits within the range from the previous studies using different light.  The researchers compared this explosion, known as a Seyfert flare, to someone turning on a galactic-sized lighthouse beam, although it would have had to shoot out cones of radiation in opposite directions and not spin.

Studies like these help astronomers learn about how both black holes and entire galaxies evolve, which might also give us a better glimpse at the larger environment our solar system grew up in, out in the Milky Way's boonies, but let's bring things most of the way back home to Enceladus, the moon of Saturn with a giant sub-surface ocean that represents one of the most promising places to look for life beyond Earth.

Astronomers have been poring over data collected by the Cassini mission for years now, looking at its observations of Enceladus to determine the exact chemical makeup of that ocean, and last month, a team based in Germany announced that they'd found evidence of the building blocks of the building blocks of life.  Amino acids make up the proteins in our bodies, but even they are made up of smaller chemical units, and the team published evidence of those more basic components.

One component has to have nitrogen, that's the amino part.  Another has to have oxygen, the acid part, and the other component varies depending on which amino acid we're talking about.  Many (?~2:57) structure that has a closed loop of atoms bonded to each other, what chemists call an aromatic ring, and the team detected all three of these in Cassini's data.  

Now, Cassini didn't get this data by looking at the ocean itself.  It's under a fair bit of ice, but lucky for us, Enceladus spits out plumes of water vapor and ice grains from its ocean into space.  Those plumes carry along any other chemicals that have been mixed in.  That can include dissolved bits of rocks and minerals, but the really interesting compounds are organic, or carbon-based molecules.

It's hypothesized that Enceladus' ocean has hydrothermal vents much like the ones here on Earth, and these vents provide the energy needed for chemical reactions to take place, including those that can create organic molecules.  Last year, the same team found evidence of larger, more complex organic molecules, but those molecules aren't very water soluble.  This time, looking at the data some more, they were able to find evidence of much smaller molecules that do dissolve in water, and that matters, because it tells us about how those bigger molecules could be made from scratch deep underwater.

To identify the compounds, the team compared over 700 measurements Cassini collected, with the signatures of all the different compounds mixed together against experiments performed on Earth.  That can't tell us the exact molecules that exist under Enceladus' surface, but it does tell us what elements and small groups of elements they're made up of.  Combined with additional information about Enceladus and how different molecules act in such environments, they narrowed down the best candidates.

As for whether amino acids can be made from those ingredients in that environment, previous studies suggest that the hydrothermal environment at the bottom of Enceladus' ocean may be similar to a region under Earth's mid-Atlantic ocean, and down there, scientists have found evidence that amino acids can form.  We're still a long way from finding even the simplest life on another world, but research like this might be inching us closer.

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