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A dwarf galaxy crashing through the Milky Way billions of years ago could have set off periods of star formation, and astronomers recently captured a rare flashing phenomenon that only shows up in the sky for a few days!

Hosted by: Hank Green

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Sources:
https://www.nature.com/articles/s41550-020-1097-0
https://www.esa.int/Science_Exploration/Space_Science/Gaia/Galactic_crash_may_have_triggered_Solar_System_formation
https://archive.vn/20161215133821/https://www.scientificamerican.com/article/sagittarius-satellite-spiral/
https://sci.esa.int/web/gaia/-/28820-summary
https://iopscience.iop.org/article/10.3847/2041-8213/ab8cc7
https://www.eurekalert.org/pub_releases/2020-05/nu-acn052620.php

Image Sources:
Thumbnail credit: Gabriel Pérez Díaz, SMM (IAC)"
https://www.videoblocks.com/video/butterfly-flaps-its-wings-close-up-of-an-alpha-channel-vcabm1otlim46opjg
https://www.istockphoto.com/vector/tornado-hurricane-3d-vector-icon-set-gm1179999726-330404909
https://www.videoblocks.com/video/butterflies-on-a-transparent-background-rgnhzwr3rk39ryfad
http://www.esa.int/ESA_Multimedia/Images/2018/09/The_Sagittarius_dwarf_galaxy_in_Gaia_s_all-sky_view
https://sci.esa.int/web/gaia/-/galactic-crash-may-have-triggered-solar-system-formation
https://sci.esa.int/web/gaia/-/51976-gaia-scanning-the-sky
https://commons.wikimedia.org/wiki/File:Gaia_Milky_Way_star_density_map_2015-07-03.png
https://images.nasa.gov/details-PIA21461
https://svs.gsfc.nasa.gov/11541
https://www.eurekalert.org/pub_releases/2020-05/nu-acn052620.php
https://commons.wikimedia.org/wiki/File:Teleskopy_ASAS_OGLE.jpg
https://news.northwestern.edu/stories/2020/05/astrophysicists-capture-new-class-of-transient-objects/&fj=1
This episode is sponsored by The Ridge.

Go to ridge.com/scishow and use promo code “scishow” to get 10% off your next order. {♫Intro♫}. You’ve probably heard of the butterfly effect.

It’s the idea that tiny actions can set off big, seemingly-unrelated events — like, how a butterfly flapping its wings in your hometown could lead to a tornado far away. And while butterflies aren’t responsible for all the extreme weather in the world, the general idea of small inputs affecting big systems is true. So now... imagine that the butterfly is a whole galaxy.

And instead of flapping its wings, it’s crashing through the Milky Way. Doesn’t really sound the same, does it? But according to research published last week in the journal Nature Astronomy, that act billions of years ago might be the reason you are around to watch this video today.

Or, at least, it might be the reason the Sun exists. Which was an important step! The study looked at how collisions with a dwarf galaxy named Sagittarius have shaped the Milky Way throughout history.

Sagittarius orbits so close to the Milky Way that scientists believe the two have actually collided three times over the last six billion years. But for this study, astronomers didn’t look at the dwarf galaxy itself. Instead, they tracked its effect on the stars around us.

And to do that, there was no better tool than the European Space Agency’s Gaia satellite, which launched in 2013. In astronomy, most missions are designed to study what something is, but Gaia performs astrometry, which measures where an object is and how it’s moving. Specifically, it measures the precise positions, distances, and velocities of more than a billion nearby stars.

That’s incredibly powerful because, if you know how something is moving, you can basically turn back the clock to see where it must have come from. In this new study, researchers noticed three clear periods of past star formation in the. Milky Way, each corresponding to one of the collisions with Sagittarius.

The oldest encounter happened about 5.7 billion years ago, and it seems to have triggered a period of star formation around the time the Sun would have been forming. Since this was all billions of years ago, proving a direct connection to the Sun is probably impossible. But this does give astronomers a plausible scenario to explain what could have happened.

As Sagittarius sloshed through, its gravity would have stirred up the Milky Way’s huge clouds of gas and dust. And parts of those clouds would have suddenly become dense enough to collapse into the start of a new star. What’s more, since Sagittarius is so much smaller than the Milky Way, the gravity from our galaxy would have stolen some of its gas and dust with every collision.

That means that the Sun—and maybe even the Earth—could be made, at least in part, of material from another galaxy. In other space news, we also found out last week that astronomers have observed a rare and mysterious event called a Fast Blue Optical Transient, or FBOT. That’s just a fancy way of saying that a funny-looking blue spot suddenly appeared in the night sky.

It wasn’t bright enough to see with your naked eye, but astronomers and their observatories noticed pretty quickly. We’ve detected a handful of these things before, but in a paper published in the Astrophysical. Journal Letters on May 26, the researchers announced that they were able to study an.

FBOT using radio waves and X-rays for just the third time. So, uh, what are these things? That’s the next big question.

We first realized these events were in a category of their own in 2014, but observing them is a challenge: They reach maximum brightness in only a few days, which makes it hard to coordinate an observing campaign among multiple telescopes. They also seem to happen in small, unremarkable galaxies we aren’t really focusing on. In fact, astronomers didn’t even know about the galaxy this one was in until the burst happened.

One thing we do know, though, is that FBOTs are powerful. This new event, for example, accelerated material weighing up to ten percent the Sun’s mass to more than 55% the speed of light. So that’ like accelerating a collection of particles heavier than a hundred Jupiters to around 160 million meters per second.

It takes a truly violent event to get so much stuff moving so quickly. And in the new paper, the researchers conclude that the most likely cause of FBOTs is a rare kind of supernova that comes from the explosion of an extra-heavy star. That might explain why we keep seeing these things in tiny galaxies: Dwarf galaxies typically have a higher fraction of hydrogen and helium than their larger counterparts.

If the galaxy has more hydrogen, so do its stars, and that actually reduces the amount of mass they lose over their lifetime. So, the end result is a bigger star and a more powerful explosion when it finally dies. As always, it would help to see more FBOTs and gather more evidence, but there’s hope here, too: While only a few dozen have been confirmed, astronomers suspect that old data probably contains evidence of many more bursts like this.

Both these discoveries illustrate the big advantage that specialized tools can offer. This latest FBOT was first observed by an automated telescope designed to search for supernovas. And Gaia’s astrometric measurements are like nothing else currently being produced.

So, while the super famous Hubble Space Telescope can take some amazing pictures, it can’t do all the work by itself. And fortunately, it doesn’t have to. Thanks for watching this episode of SciShow Space News!

This week’s news is sponsored by The Ridge, the makers of The Ridge Wallet. The wallet is designed to be sleek and light, but also hold everything you need—assuming you need up to a dozen cards plus cash. It comes in more than 30 colors and styles and also comes with a lifetime warranty.

If you want to learn more, The Ridge is offering a 45-day test-drive where you can try the wallet and see what you think. And if you don’t love it, you can send it back for a full refund. If you’re interested, you can get 10% off and free worldwide shipping by going to ridge.com/SCISHOW and using the promo code “SCISHOW.” When you support our sponsors, you’re also helping us make more episodes like this one.

So thanks for considering it! {♫Outro♫}.