3 Ways to Slingshot a Star

3 Ways to Slingshot a Star

Thanks to CuriosityStream for supporting this
episode! Go to CuriosityStream.com/Space to learn more. [♪ INTRO] The star-mapping satellite Gaia has been scanning
the sky for five years now, building a catalog that should reach one billion stars. Given all that data, it makes sense that Gaia
has found some weird stuff. And in the middle of it all, astronomers have
singled out over 20 stars speeding across the Milky Way
toward intergalactic space. And stars don’t usually do this! The galaxy has a lot of gravity to keep stuff
in. But there are a few things that can slingshot
a star out of a galaxy. And whatever the case, it takes some extreme
gravitational interactions. Normal stars travel around the galaxy at a
casual 1 million kilometers an hour or so. But some of the fastest stars making their
escape are moving over three times as fast, and many of them seem to be coming from the
same place: the center of our galaxy. Sitting there, keeping everything glued together, is a supermassive black hole called Sagittarius A*, or Sag A* for short. It’s surrounded by a huge, dense region
of star formation. With such extreme gravity keeping all the
gases nice and compact, some of those gases condense and ignite to become stars. So you get a lot of stars forming close together,
and that means you end up with lots of pairs or groups of stars orbiting each other while
they also circle Sag A*. So let’s take the case of a binary star
system going around the black hole. If they’re too close to the black hole to
have a stable orbit, the stars will spiral inward toward it. And at a certain point, the black hole’s
gravity will overcome the gravitational bond between the two stars and pull them apart. The innermost star will be swept into a tighter orbit around the black hole, pulled away from its companion. But here’s the thing, those two stars orbiting
each other have a ton of energy between them. There’s kinetic energy in their orbital
motion and potential energy in their gravitational bond. So when half of that system disappears, the energy
doesn’t disappear with it. Because energy in a system is always conserved! So when its partner leaves that binary star
system and gets captured by the black hole, the remaining star suddenly gets all that
energy, which gives it a giant kick across the galaxy. This process is an example of what’s called
dynamical ejection. But only about half of the galaxy’s fastest-moving
stars are coming from the center, so they can’t all be survivors of the black hole. There has to be something else going on to
explain how all those other stars got moving so fast. And it looks like there is. It starts with a Sun-like star in a binary
system with a gigantic companion. These systems can exist anywhere in the galaxy. And one day, the huge companion star explodes
into a supernova. To understand what happens next, imagine a
ball on a string: you’re holding one end and whirling the ball around over your head. And then the string breaks. The ball sails off in a straight line. And the faster you’re whirling it around,
the faster it flies off. And that’s exactly what happens to the smaller
companion star. Before the explosion, there’s a gravitational
bond between the two stars that holds them together like a string. When one star bursts into a supernova, its
mass gets scattered into space. That essentially “breaks the string” of
the gravitational bond. Without any mass tying it down, the remaining
star goes sailing toward interstellar space, moving as fast as it used to orbit its old
companion. This is called binary ejection. And binary ejection probably accounts for
most of the smaller, older stars that are on their way out of the galaxy. So that explains most of the stars that are
leaving the galaxy. But it still can’t explain everything. So, finally, one last mechanism for slingshotting a star. This one is another type of dynamical ejection,
but it doesn’t happen in the center of the galaxy. Instead, it seems to happen when a star is
booted out of its star cluster. That can happen sometimes, because, in a dense
cluster, stars are getting pulled around on all sides by the gravity of their neighbors, and everything is exchanging a lot of energy. For instance, a star might swing close to
a binary pair and get swept up in a chaotic 3-body orbit. It might split off with one member of the
pair, or the stars might all end up as single stars. In the process, a lot of energy gets traded around,
and under just the right conditions, a star can pick up enough energy to get kicked out
of the cluster. Astronomers discovered an extreme example
of this phenomenon in 2014, when they found a star eight times as big as the Sun traveling about twice as fast as other stars in the galaxy. Hurling such a massive star across the galaxy
at that speed takes serious energy. And astronomers think it got ejected from
a really dense star cluster. This star was an outlier because of its size, but ejections like this happen on smaller scales pretty often, and they’re probably behind many of the other stars speeding across the galaxy. The fact that these extreme gravitational
interactions are relatively common in our galaxy suggests that there are lots of rogue
stars flying through intergalactic space, booted from their home galaxies. Fortunately, Gaia and other surveys are still
gathering tons of good data, so we’ll probably see plenty more weird stuff soon! If you’re interested in learning more about some of the most extreme gravitational interactions in our universe, you might like the CuriosityStream
documentary “Knowing Without Seeing.” It’s all about black holes and how the more
scientists learn about them, the more mysteries they open up. And if science documentaries are your thing, CuriosityStream has over 2,400 of them for you to explore, including exclusive originals. They cover a whole range of topics, including
science, nature, history, technology, and others. You can get unlimited access for as little
as $2.99 a month, and since you’re a SciShow viewer, you can get the first month free if
you sign up at curiositystream.com/space and use the promo code “space.” [♪ OUTRO]

About the author


  1. Go to http://curiositystream.com/Space to start streaming Knowing Without Seeing. Use the promo code โ€˜spaceโ€™ during the sign-up process to get your first 31 days free.

  2. Hello Thank you for the video, is the speed of light is a constant?

    There is no argument about the speed that fluctuates between psychical mediums, But for example, we assume that the speed of light near Alpha Centauri is the same as the speed of light here on Earth. what I'm saying is we just assuming it, we don't know about that right, do we?

    The facts are that we cannot know what is going on everywhere in the universe, so we cannot determine that the speed of light (electromagnetic wave speed) is constant!

    *As a matter of principle, this should be taken into account, since it is logical from a lack of evidence!

    We can assume different possibilities, (just like we assuming that it is constant), what if light is emitted from someplace near us.

    maybe it emitted from the center of the earth.

    and maybe is emitted from life. maybe there is million more possibility?

    maybe after you laugh for a few seconds you will maybe realize that this is not a completely unbelievable idea as it can dismiss some paradoxes in Quantum Physics

    science it is not a game in make believe!

    What I am saying is that we have no way of checking it out!

    If we only checked in one place in the entire universe! It's kind of ridiculous to say that.

    So this is actually a question of right or wrong!

    So basically because we can't be sure about it, regardless of right, or wrong! and so do about 50% of the models as if the speed of light is not constant!

  3. It boggles the mind to attempt to think about the massive forces involved – you'd think the ejected star would be ripped to shreds by the acceleration.

  4. Black holes dont exist. Stars at the center of the galaxy are shot out electrically. You people assume its binary stars flinging each other.

  5. Could dense wall of a pressurized room and some reduce enursa. On sudden accelerations. As room with the humans is very dense Walls

  6. The universe is inconceivably ginormous. Sad to think that humans will never be able to travel out of this star system because of how short our lifespans are.

  7. Wonder if intergalactic space is best place for life. Not likely. Well look at our own solar system. Intergalactic space would have the least radiation

  8. Those damned Hollywood ruffians in their souped up hot rods!
    Just cause your a star, don't think you can't get a ticket!

  9. "First, you gotta get a really, REALLY big rubber band…"

    Haven't watched the video yet, or read the other comments, but I just had to say that, sorry

  10. I had to look up the word "dynamical" because it sounded odd. I found out that "dynamical" is the adjective form of "dynamic"… which itself is an adjective. So "dynamical" is the adjective form of the adjective "dynamic". How far we have advanced!

  11. Umass Amherst helped take one of those pictures for this video? Lol. I thought that entire campus was drowning in a sea of booze and depressed students.

  12. i have to wonder if it is at all possible for an ejected star to hold on to any of its planets, or if ejecting them is part of the boost that they get.

  13. Sorry, hang on a second… 1 million km ~= 621371.2 mph?

    There's a mismatch with Digits here, and it's Significant.

  14. A bit of advice for any of you youngstars out there who might've been kicked out of your galaxy cluster and are thinking that leaving your home galaxy on a high-speed joy-ride looks like fun: Just REMEMBER – keeping that speedometer under 670,616,629 miles per hour is not only a GOOD idea …it's also the LAW!

  15. I felt like a third star joining a binary could be a metaphor for some relationships. Also I wonder what happens when two binary systems interact.

  16. I thought that when a star went supernova, it either becomes a black hole or a neutron star. If that's correct, then would the twin not continue to interact in orbit with the black hole as it did the star? I just think that if the twin was close enough to the supernova that it was ejected by it, it would've been way too close during the stars rapid expansion prior to going nova and the whole thing would've been over at that point.

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