A meteor drought, a meteor strike, and a trio of merging galaxies

By on November 22, 2019 in

Last night’s meteor shower was a bust. We’re sorry we sent you outside to watch. Since we can’t report on that, we tell you instead about new research providing new age information on Wolf Creek Crater. We also discuss the NGC 6240 merger of 3 systems.

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Yesterday, we encouraged anyone with clear skies to go outside a look up because there was supposed to be meteor storm. If, like me, you had terrible cloud, you may have been sad about missing the opportunity to see as many as 7 meteors a minute falling out the sky. Well, despair no more. Last night’s so called Alpha Monocertids meteor storm was more like a meteor drought. European space journalist Daniel Fischer reported that an experienced meteor observer in Bavaria had seen a slight enhancement in activity with a 5 minute peak in activity between 4:55 and 5:00 UT. If you weren’t an experienced meteor watcher… you likely were sad. And if you were clouded in and sad, hopefully you are sad no more.

On the topic of rocks falling out of the sky, a new paper in Meteoritics and Planetary Science details how the aging of soils and rocks around the Wolf Creek crater in Western Australia has allowed new age estimations to be made, and when looked at in the context of all the craters on the arid parts of Australia, allows new cratering rates to be calculated. Here’s how this works. When a roughly 15-m across and 14,000 ton rock fell out of the sky and hit what is now Western Australia, a 900m across crater was formed, and during the impact sedimentary layers were flipped. This exposed rock that had been previously shielded from cosmic rays, and also shielded previously exposed layers. When they measured how long ago the exposed rock had been exposed, and when the shielded rock was shielded, they got two ages that matched within error, and they indicate the crater was formed roughly 120,000 years ago. At this point in pre-history, humans existed in their modern form, but it isn’t believed that they had reached the Island continent of Australia yet. Still, the site of this massive rock flying through the sky may have traumatized some of our most ancient ancestors.

Wolf Creek Crater is the largest of many craters that dot the surface of Australia. All together 7 impact events are preserved in the arid outback. By considering how much of the world’s total surface area that land represents, it becomes possible to work out the rate at which new large craters are forming, and that rate is a whole lot higher than many of us were taught. They believe that potentially crater forming impacts may occur every 180 years or so. This seems consistent with what we’ve seen, if you consider the Tunguska air explosion in 1908 and the Chelyabinsk event in 2013. Since the Earth’s surface is mostly water, we also don’t know what events like these we simply missed in the days before satellites. 

So, the sky is falling, just not when you are watching for the Alpha Monocertids.

Switching gears completely, newly published observations of the massive and irregularly shaped galaxy NGC 6240 uncover the existence of 3 supermassive black holes in its core. Imaged in visible light, this system is a tangle of dust, glowing gas, and star formation, and is clearly the trainwreck that results from galaxies colliding a merging. It has long been assumed that this was the result of two systems coming together to form a new and larger galaxy. When the motions of this gas are measured with the high resolution MUSE spectrograph on the Very Large Telescope in Chili, the presence of 3 massive black holes is resolved. This is the first time such a trio of masses has been seen, and changes our perspective on galaxy mergers. He had been thought that massive systems general merge pair-wise, but if the most massive systems in our universe have to form 1 merger at a time, it becomes difficult to explain how we ended up with so many massive systems in our modern universe. If instead, it is fairly common for things to come together in groups of 3 or maybe even more, massive systems can form much faster, and our universe makes a lot more sense. At this time, we don’t know how often these many-galaxy collisions take place and more observations of more massive irregular galaxies are needed. Beyond being the target of MUSE and other high resolution spectrographs, systems like this will also potential be observational targets of the future LISA gravitational wave detector that should be launched into orbit in the coming years. It’s thought this galaxy will merge its black holes in a few million years, and it’s possible similar systems are out there and primed to complete their merger when LISA is ready to listen.

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And that rounds out our show for today.

Thank you all for listening. The Daily Space is produced by Susie Murph, and is a product of the Planetary Science Institute, a 501(c)3 non profit dedicated to exploring our Solar System and beyond. We are here thanks to the generous contributions of people like you. Want to become a supporter of the show? Check us out at Patreon.com/cosmoquestx

Each live episode of the Daily Space is archived on YouTube. If you miss an episode on Twitch.tv, you can find it later on youtube.com/c/cosmoquest. These episodes are edited and produced by Susie Murph. 

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About Susie Murph

Susie Murph is a Communications Specialist at CosmoQuest. She produces the Astronomy Cast, the Weekly Space Hangout and Daily Space.

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