APOD: Runaway Star Alpha Camelopardalis (2023 Apr 28)

[APOD Robot]

Runaway Star Alpha Camelopardalis

Explanation: Like a ship plowing through cosmic seas, runaway star Alpha Camelopardalis has produced this graceful arcing bow wave or bow shock. The massive supergiant star moves at over 60 kilometers per second through space, compressing the interstellar material in its path. At the center of this nearly 6 degree wide view, Alpha Cam is about 25-30 times as massive as the Sun, 5 times hotter (30,000 kelvins), and over 500,000 times brighter. About 4,000 light-years away in the long-necked constellation Camelopardalis, the star also produces a strong stellar wind. Alpha Cam's bow shock stands off about 10 light-years from the star itself. What set this star in motion? Astronomers have long thought that Alpha Cam was flung out of a nearby cluster of young hot stars due to gravitational interactions with other cluster members or perhaps by the supernova explosion of a massive companion star.

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[shaileshs]

People talk about many possible galactic (non human made) reasons/ways of Earth getting destroyed (e.g. CME, Asteroid, Gamma Ray burst, Disruption of layers in atmosphere saving us from X-ray radiation, Sun getting bigger in 5B years and gulping earth.. etc etc etc). I wonder if anyone has thought about some such random BIG runaway star directly shooting towards us at high velocity in a relatively nearby sky ? I mean there are ways to deflect an asteroid (decent size, detected early) but how do we avoid collision course with such runaway powerful big star ? No known solution I'd imagine except preparing for impact assuming we detect it early enough and have some time - maybe a few years - to prepare and count down to doomsday ? Thanks in advance for all comments/answers.

[Ann]

Blue eyed Alpha Cam R B composite DSS2.png (162.1 KiB) Viewed 7788 times

I am blue-eyed Alpha Cam! Nice to meet you!

Alpha Cam at the top of the diagram.png (59.17 KiB) Viewed 7788 times

Alpha Cam is at the top of the color magnitude diagram!

Alpha Cam is a magnificent star! Just look at that color-magnitude diagram with Alpha Cam at top! This star is a blue supergiant.

Now that introductions are over with, let's look at a gallery of hot blue runaway stars with bow shocks!

O9Ia supergiant star Alpha Cam and bow shock. Credit: NASA/JPL/Caltech/WISE

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Located about 440 light-years from Earth, O9.5V star Zeta Ophiuchi is a hot star that is 20 times more massive than the Sun. Previous observations have provided evidence that Zeta Ophiuchi was once in close orbit with another star, before being ejected at about 100,000 miles per hour when this companion was destroyed in a supernova explosion over a million years ago. Previously released infrared data from NASA's now-retired Spitzer Space Telescope, seen in this new composite image, reveals a spectacular shock wave (red and green) that was formed by matter blowing away from the star's surface and slamming into gas in its path. Data from Chandra shows a bubble of X-ray emission (blue) located around the star, produced by gas that has been heated by the effects of the shock wave to tens of millions of degrees. Image credit: X-ray: NASA/CXC/Dublin Inst. Advanced Studies/S. Green et al.; Infrared: NASA/JPL/Spitzer

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B0.7 Ia supergiant star Kappa Cassiopeiae and its bow shock. Image: NASA/JPL-Caltech

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O7.5III giant star Xi Persei and its bow shock, the California Nebula. Image: John Corban & the ESA/ESO/NASA Photoshop FITS Liberator

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B0.5Ia supergiant star HD77581 and its optically invisible X-ray companion creating a perfect bow shock. Credit: ESO

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All the stars in this gallery are runaway stars, pushing interstellar material in front of them and adding their own winds, too. So how do stars become runaways? Well, it typically involves a binary system that comes into contact with another compact gravitational source in such a way that the binary is broken up, and one component gets a huge kick and is flung away.

The fastest known runaway star in the Milky Way is S5-HVS1.

Wikipedia wrote:

S5-HVS1 is an A-type main-sequence star notable as the fastest one detected as of November 2019, and has been determined to be traveling at 1,755 km/s (3,930,000 mph). The star is in the Grus (or Crane) constellation in the southern sky, and about 29,000 light-years from Earth. According to astronomers, S5-HVS1 was ejected from the Milky Way galaxy after interacting with Sagittarius A*, the supermassive black hole at the center of the galaxy.[1][2] It is possible that it was originally part of a binary system that was tidally disrupted by the supermassive black hole, causing it to be ejected. If this is the case, that it was flung out of the galaxy by the central black hole, it is then the first example of a star that has undergone the Hills mechanism.

If you go to this page, you can see a cool animation of what it might have looked like when S5-HVS1 was ejected.

Ann

[zendae]

So let's say S5-HVS1 had a couple planets. Are they still in capture by the star hurtling thru space, or has all the upheaval overcome the gravity that held them? Have they become runaway planets, now alone in the dark?

[Chris Peterson]

So let's say S5-HVS1 had a couple planets. Are they still in capture by the star hurtling thru space, or has all the upheaval overcome the gravity that held them? Have they become runaway planets, now alone in the dark?

It's perfectly possible for a star to be ejected from a cluster or star forming region and retain its planets, although the tidal forces might well alter the orbits of those planets.

[Chris Peterson]

People talk about many possible galactic (non human made) reasons/ways of Earth getting destroyed (e.g. CME, Asteroid, Gamma Ray burst, Disruption of layers in atmosphere saving us from X-ray radiation, Sun getting bigger in 5B years and gulping earth.. etc etc etc). I wonder if anyone has thought about some such random BIG runaway star directly shooting towards us at high velocity in a relatively nearby sky ? I mean there are ways to deflect an asteroid (decent size, detected early) but how do we avoid collision course with such runaway powerful big star ? No known solution I'd imagine except preparing for impact assuming we detect it early enough and have some time - maybe a few years - to prepare and count down to doomsday ? Thanks in advance for all comments/answers.

Just an ordinary solar mass star passing slowly within a light year or so of us would be sufficient to disrupt the orbits of our planets, which is all it would take to do us in.

[Ann]

So let's say S5-HVS1 had a couple planets. Are they still in capture by the star hurtling thru space, or has all the upheaval overcome the gravity that held them? Have they become runaway planets, now alone in the dark?

It's perfectly possible for a star to be ejected from a cluster or star forming region and retain its planets, although the tidal forces might well alter the orbits of those planets.

I'm not arguing (very much), Chris, but note that all but one of the more nearby runaway stars that I showed pictures of in my "gallery" appear to be single.

Wikipedia wrote about Alpha Cam:

In 1968, this star was classified as a spectroscopic binary, indicating that it has an orbiting stellar companion with a period of 3.68 days and an orbital eccentricity of 0.45. Subsequent studies refined the period to 3.24 days. However, in 2006 it was recognized that the changes in the spectrum were probably the result of changes in the atmosphere or stellar wind, so it is more likely a single star.[11] Speckle interferometry observations with the 3.67 m Advanced Electro Optical System Telescope at the Haleakala Observatory failed to detect a secondary component.

Wikipedia wrote about Zeta Ophiuchi:

Zeta Ophiuchi (ζ Oph, ζ Ophiuchi) is a single star located in the constellation of Ophiuchus.

Wikipedia wrote about AE Aurigae:

Possibly due to its runaway star nature, AE Aurigae has no physical companion stars, although some nearby stars have been erroneously identified as ones.

Wikipedia doesn't say that Xi Persei is single, but nothing is said about any companions. Wikipedia also doesn't say that Kappa Cassiopeiae is single, but again, nothing is said about a companion.

However, Vela X-1 is a binary system consisting of blue supergiant star HD 77581 and a neutron star. This is a runaway system, so clearly it is possible for gravitationally bound systems to remain bound even after they have received a gravitational kick and become runaways.

My point, nevertheless, is that massive runaway stars often appear to be single, whereas massive "non-runaway stars" are more often multiple.

Take the bright blue stars of constellation Orion, for example. Rigel is multiple. Alnitak is multiple. Mintaka, Delta Orionis, is multiple. Meissa, Lambda Orionis, is multiple. However, Saiph, Alnilam and Bellatrix have no known companions.

So it seems to me that runaway stars appear to be single more often than stars that are not runaways. Of course, whether that has anything to do with a star's ability to hold on to its own planets when it receives a huge gravitational kick is beyond my poor mathematical understanding.

Ann

[Chris Peterson]

So let's say S5-HVS1 had a couple planets. Are they still in capture by the star hurtling thru space, or has all the upheaval overcome the gravity that held them? Have they become runaway planets, now alone in the dark?

It's perfectly possible for a star to be ejected from a cluster or star forming region and retain its planets, although the tidal forces might well alter the orbits of those planets.

I'm not arguing (very much), Chris, but note that all but one of the more nearby runaway stars that I showed pictures of in my "gallery" appear to be single.

I don't know what you mean by "single". We would be unlikely to be able to detect if any of these stars have planetary systems.

[johnnydeep]

It's perfectly possible for a star to be ejected from a cluster or star forming region and retain its planets, although the tidal forces might well alter the orbits of those planets.

I'm not arguing (very much), Chris, but note that all but one of the more nearby runaway stars that I showed pictures of in my "gallery" appear to be single.

I don't know what you mean by "single". We would be unlikely to be able to detect if any of these stars have planetary systems.

Ann seems to mean stars that are not "multiple"s, as in binaries, trinaries, etc. But holding on to planets seems like it would be a lot easier than holding on to a much more massive fellow stellar sibling?

[johnnydeep]

There seems to be some uncertainty in knowing how fast this star is travelling. The APOD text says 60 km/s, but the WISE link says

Such fast-moving stars are called runaway stars. The distance and speed of Alpha Cam is somewhat uncertain. It is probably somewhere between 1,600 and 6,900 light-years away and moving at an astonishing rate of somewhere between 680 and 4,200 kilometers per second (between 1.5 and 9.4 million mph).

[orin stepanek]

Not hard to imagine a rough Star having a planetary system!
imagine living on such a planet?

[Ann]

I'm not arguing (very much), Chris, but note that all but one of the more nearby runaway stars that I showed pictures of in my "gallery" appear to be single.

I don't know what you mean by "single". We would be unlikely to be able to detect if any of these stars have planetary systems.

Ann seems to mean stars that are not "multiple"s, as in binaries, trinaries, etc. But holding on to planets seems like it would be a lot easier than holding on to a much more massive fellow stellar sibling?

Yes, Johnny, that's what I meant.

And I agree that in most cases it would seem easier for a star to hold on to its planets than to hold on to its stellar partner. Of course, it would depend on the makeup of the binary and the planetary system(s).

When binary stars are similar in mass (left), the two stars orbit the system’s center of mass (denoted here with an X). Planets in an S-type orbit circle just one star in the system, while planets in a P-type orbit revolve around both stars together. When one star far outweighs the other (right), the smaller star orbits the larger one. A planet in a T-type orbit would share the orbit of the smaller companion around the larger star, locked into one of two positions — the L4 or L5 Lagrangian points — ahead of or behind the smaller star. Credit: Astronomy: Roen Kelly

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Astronomy Magazine wrote:

Q: Can solar systems exist in a binary star system? If so, what kind of orbital patterns would the planets and moons have around the two suns?

Amanda Stewart
Auckland, New Zealand


A: Yes, planetary systems can exist in binary star systems. As of July 2019, astronomers have found 97 planetary systems containing 143 planets around binary stars. These planets may orbit just one of the stars in the binary system, called an S-type (satellite-type) orbit, or they can orbit both stars together from outside the binary, called a circumbinary or P-type (planet-type) orbit. Most of the known planets in binary systems have S-type orbits, in which they orbit close to one star and essentially ignore the companion star, which is farther away.

There is a third option, although no planets with this type of orbit have been found yet: a T-type orbit. In this configuration, one star in the pair is much smaller than the other. The smaller star orbits the larger star and the planet shares the orbit with the smaller star, gravitationally locked into a position either 60° ahead of or 60° behind the smaller star. These positions are called Lagrangian points. Planets in T-type orbits are sometimes called Trojan planets — just like the Trojan asteroids, for example, that share Jupiter’s orbit around the Sun.

Alison Klesman
Associate Editor

[zendae]

I don't know what you mean by "single". We would be unlikely to be able to detect if any of these stars have planetary systems.

Ann seems to mean stars that are not "multiple"s, as in binaries, trinaries, etc. But holding on to planets seems like it would be a lot easier than holding on to a much more massive fellow stellar sibling?

Yes, Johnny, that's what I meant.

And I agree that in most cases it would seem easier for a star to hold on to its planets than to hold on to its stellar partner. Of course, it would depend on the makeup of the binary and the planetary system(s).

But I wonder about that. A star with a stellar companion works both ways, does it not? Ergo, each star is holding on to the other gravitationally. Wouldn't that be a strong bond, almost a synergistic one, able to handle more upheaval than a star/planet combo?

When binary stars are similar in mass (left), the two stars orbit the system’s center of mass (denoted here with an X). Planets in an S-type orbit circle just one star in the system, while planets in a P-type orbit revolve around both stars together. When one star far outweighs the other (right), the smaller star orbits the larger one. A planet in a T-type orbit would share the orbit of the smaller companion around the larger star, locked into one of two positions — the L4 or L5 Lagrangian points — ahead of or behind the smaller star. Credit: Astronomy: Roen Kelly

---

Astronomy Magazine wrote:

Q: Can solar systems exist in a binary star system? If so, what kind of orbital patterns would the planets and moons have around the two suns?

Amanda Stewart
Auckland, New Zealand


A: Yes, planetary systems can exist in binary star systems. As of July 2019, astronomers have found 97 planetary systems containing 143 planets around binary stars. These planets may orbit just one of the stars in the binary system, called an S-type (satellite-type) orbit, or they can orbit both stars together from outside the binary, called a circumbinary or P-type (planet-type) orbit. Most of the known planets in binary systems have S-type orbits, in which they orbit close to one star and essentially ignore the companion star, which is farther away.

There is a third option, although no planets with this type of orbit have been found yet: a T-type orbit. In this configuration, one star in the pair is much smaller than the other. The smaller star orbits the larger star and the planet shares the orbit with the smaller star, gravitationally locked into a position either 60° ahead of or 60° behind the smaller star. These positions are called Lagrangian points. Planets in T-type orbits are sometimes called Trojan planets — just like the Trojan asteroids, for example, that share Jupiter’s orbit around the Sun.

Alison Klesman
Associate Editor

[Chris Peterson]

I don't know what you mean by "single". We would be unlikely to be able to detect if any of these stars have planetary systems.

Ann seems to mean stars that are not "multiple"s, as in binaries, trinaries, etc. But holding on to planets seems like it would be a lot easier than holding on to a much more massive fellow stellar sibling?

Yes, Johnny, that's what I meant.

And I agree that in most cases it would seem easier for a star to hold on to its planets than to hold on to its stellar partner. Of course, it would depend on the makeup of the binary and the planetary system(s).

When binary stars are similar in mass (left), the two stars orbit the system’s center of mass (denoted here with an X). Planets in an S-type orbit circle just one star in the system, while planets in a P-type orbit revolve around both stars together. When one star far outweighs the other (right), the smaller star orbits the larger one. A planet in a T-type orbit would share the orbit of the smaller companion around the larger star, locked into one of two positions — the L4 or L5 Lagrangian points — ahead of or behind the smaller star. Credit: Astronomy: Roen Kelly

---

Astronomy Magazine wrote:

Q: Can solar systems exist in a binary star system? If so, what kind of orbital patterns would the planets and moons have around the two suns?

Amanda Stewart
Auckland, New Zealand


A: Yes, planetary systems can exist in binary star systems. As of July 2019, astronomers have found 97 planetary systems containing 143 planets around binary stars. These planets may orbit just one of the stars in the binary system, called an S-type (satellite-type) orbit, or they can orbit both stars together from outside the binary, called a circumbinary or P-type (planet-type) orbit. Most of the known planets in binary systems have S-type orbits, in which they orbit close to one star and essentially ignore the companion star, which is farther away.

There is a third option, although no planets with this type of orbit have been found yet: a T-type orbit. In this configuration, one star in the pair is much smaller than the other. The smaller star orbits the larger star and the planet shares the orbit with the smaller star, gravitationally locked into a position either 60° ahead of or 60° behind the smaller star. These positions are called Lagrangian points. Planets in T-type orbits are sometimes called Trojan planets — just like the Trojan asteroids, for example, that share Jupiter’s orbit around the Sun.

Alison Klesman
Associate Editor

It is worth noting that, with the possible exception of a planet orbiting a star that is very far from its companion star, none of these orbits are likely to be stable for long periods of time. So planets in binary systems are unlikely to have enough time for complex life to develop on them.

[johnnydeep]

Ann seems to mean stars that are not "multiple"s, as in binaries, trinaries, etc. But holding on to planets seems like it would be a lot easier than holding on to a much more massive fellow stellar sibling?

Yes, Johnny, that's what I meant.

And I agree that in most cases it would seem easier for a star to hold on to its planets than to hold on to its stellar partner. Of course, it would depend on the makeup of the binary and the planetary system(s).

But I wonder about that. A star with a stellar companion works both ways, does it not? Ergo, each star is holding on to the other gravitationally. Wouldn't that be a strong bond, almost a synergistic one, able to handle more upheaval than a star/planet combo?

Yeah, I thought of that possibility too. Unless the reason that one star of a binary pair was ejected was because either it or the other star went (super)nova?

[Chris Peterson]

Yes, Johnny, that's what I meant.

And I agree that in most cases it would seem easier for a star to hold on to its planets than to hold on to its stellar partner. Of course, it would depend on the makeup of the binary and the planetary system(s).

But I wonder about that. A star with a stellar companion works both ways, does it not? Ergo, each star is holding on to the other gravitationally. Wouldn't that be a strong bond, almost a synergistic one, able to handle more upheaval than a star/planet combo?

Yeah, I thought of that possibility too. Unless the reason that one star of a binary pair was ejected was because either it or the other star went (super)nova?

A planet may be much more strongly bound to its parent star than that star might be to its binary companion.

[VictorBorun]

a runaway star that left at 4200 km/s its companion and all the shared planets is breaking its vows…
Or was they like «till a sudden ejection does us part?»

[johnnydeep]

But I wonder about that. A star with a stellar companion works both ways, does it not? Ergo, each star is holding on to the other gravitationally. Wouldn't that be a strong bond, almost a synergistic one, able to handle more upheaval than a star/planet combo?

Yeah, I thought of that possibility too. Unless the reason that one star of a binary pair was ejected was because either it or the other star went (super)nova?

A planet may be much more strongly bound to its parent star than that star might be to its binary companion.

So what is the mathematical definition of the "binding strength"? Is it simply he strength of gravity at the distance of one body from the other? (Hmm, I suppose that force MUST be the same no matter which body is used as the reference point?)

[Chris Peterson]

Yeah, I thought of that possibility too. Unless the reason that one star of a binary pair was ejected was because either it or the other star went (super)nova?

A planet may be much more strongly bound to its parent star than that star might be to its binary companion.

So what is the mathematical definition of the "binding strength"? Is it simply he strength of gravity at the distance of one body from the other? (Hmm, I suppose that force MUST be the same no matter which body is used as the reference point?)

In this context, I'd say it is a measure of how much you need to change the velocity of the orbiting body in order for it to reach escape velocity. That can be very high for a planet close to its parent star, and very small for a body far from the star. Bodies in the Oort Cloud, for instance, are very, very close to escape velocity, so just the tiniest nudge by a third body can send them out of the Solar System.

[VictorBorun]

There seems to be some uncertainty in knowing how fast this star is travelling. The APOD text says 60 km/s, but the WISE link says

Such fast-moving stars are called runaway stars. The distance and speed of Alpha Cam is somewhat uncertain. It is probably somewhere between 1,600 and 6,900 light-years away and moving at an astonishing rate of somewhere between 680 and 4,200 kilometers per second (between 1.5 and 9.4 million mph).

The thing that I find strange is how WISE link's distance uncertainty (probably somewhere between 1,600 and 6,900 light-years away) did collapse to Wiki's a distance of approximately 6,000 light-years from Earth based on parallax measurements
while the runaway velocity stays exactly at a monster of a range The star is traveling at a rate of somewhere between 680 and 4,200 kilometers per second: between 1.5 and 9.4 million mph.

[johnnydeep]

A planet may be much more strongly bound to its parent star than that star might be to its binary companion.

So what is the mathematical definition of the "binding strength"? Is it simply he strength of gravity at the distance of one body from the other? (Hmm, I suppose that force MUST be the same no matter which body is used as the reference point?)

In this context, I'd say it is a measure of how much you need to change the velocity of the orbiting body in order for it to reach escape velocity. That can be very high for a planet close to its parent star, and very small for a body far from the star. Bodies in the Oort Cloud, for instance, are very, very close to escape velocity, so just the tiniest nudge by a third body can send them out of the Solar System.

Nice. I can understand that!

[javachip3]

... planets in binary systems are unlikely to have enough time for complex life to develop on them.

Tatooine orbits a binary system, and Luke, his family, and other local fauna are quite complex.

[javachip3]

... Bodies in the Oort Cloud, for instance, are very, very close to escape velocity, so just the tiniest nudge by a third body can send them out of the Solar System.

Or toward the center of the Solar System.

[javachip3]

People talk about many possible galactic (non human made) reasons/ways of Earth getting destroyed (e.g. CME, Asteroid, Gamma Ray burst, Disruption of layers in atmosphere saving us from X-ray radiation, Sun getting bigger in 5B years and gulping earth.. etc etc etc). I wonder if anyone has thought about some such random BIG runaway star directly shooting towards us at high velocity in a relatively nearby sky ? I mean there are ways to deflect an asteroid (decent size, detected early) but how do we avoid collision course with such runaway powerful big star ? No known solution I'd imagine except preparing for impact assuming we detect it early enough and have some time - maybe a few years - to prepare and count down to doomsday ? Thanks in advance for all comments/answers.

All stars of appreciable mass and luminosity within a thousand light years have been well characterized. None are on a dangerous trajectory towards us. Even if Alpha Centauri, the closest bright star to our solar system, for some reason suddenly began speeding towards us at 40 miles per second (the speed of runaway star Alpha Cam), it would take 4700 years to reach us. That's someone else's problem.

Life is more likely to exist, and to persist, in the periphery of galaxies, where celestial bodies are less crowded, and close encounters, with their gravitational disruptions, are infrequent.

[javachip3]

Blue eyed Alpha Cam R B composite DSS2.png

I am blue-eyed Alpha Cam! Nice to meet you!

Alpha Cam at the top of the diagram.png

Alpha Cam is at the top of the color magnitude diagram!

Alpha Cam is a magnificent star! Just look at that color-magnitude diagram with Alpha Cam at top! This star is a blue supergiant.

Now that introductions are over with, let's look at a gallery of hot blue runaway stars with bow shocks!

O9Ia supergiant star Alpha Cam and bow shock. Credit: NASA/JPL/Caltech/WISE

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Located about 440 light-years from Earth, O9.5V star Zeta Ophiuchi is a hot star that is 20 times more massive than the Sun. Previous observations have provided evidence that Zeta Ophiuchi was once in close orbit with another star, before being ejected at about 100,000 miles per hour when this companion was destroyed in a supernova explosion over a million years ago. Previously released infrared data from NASA's now-retired Spitzer Space Telescope, seen in this new composite image, reveals a spectacular shock wave (red and green) that was formed by matter blowing away from the star's surface and slamming into gas in its path. Data from Chandra shows a bubble of X-ray emission (blue) located around the star, produced by gas that has been heated by the effects of the shock wave to tens of millions of degrees. Image credit: X-ray: NASA/CXC/Dublin Inst. Advanced Studies/S. Green et al.; Infrared: NASA/JPL/Spitzer

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B0.7 Ia supergiant star Kappa Cassiopeiae and its bow shock. Image: NASA/JPL-Caltech

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O7.5III giant star Xi Persei and its bow shock, the California Nebula. Image: John Corban & the ESA/ESO/NASA Photoshop FITS Liberator

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B0.5Ia supergiant star HD77581 and its optically invisible X-ray companion creating a perfect bow shock. Credit: ESO

---

All the stars in this gallery are runaway stars, pushing interstellar material in front of them and adding their own winds, too. So how do stars become runaways? Well, it typically involves a binary system that comes into contact with another compact gravitational source in such a way that the binary is broken up, and one component gets a huge kick and is flung away.

The fastest known runaway star in the Milky Way is S5-HVS1.

Wikipedia wrote:

S5-HVS1 is an A-type main-sequence star notable as the fastest one detected as of November 2019, and has been determined to be traveling at 1,755 km/s (3,930,000 mph). The star is in the Grus (or Crane) constellation in the southern sky, and about 29,000 light-years from Earth. According to astronomers, S5-HVS1 was ejected from the Milky Way galaxy after interacting with Sagittarius A*, the supermassive black hole at the center of the galaxy.[1][2] It is possible that it was originally part of a binary system that was tidally disrupted by the supermassive black hole, causing it to be ejected. If this is the case, that it was flung out of the galaxy by the central black hole, it is then the first example of a star that has undergone the Hills mechanism.

If you go to this page, you can see a cool animation of what it might have looked like when S5-HVS1 was ejected.

Ann

How do we know these are runaway stars? Have their proper motions been measured? Some of the images are visually suggestive of bow shocks, but the structure around Kappa Cass looks like it could simply be a bubble caused by stellar wind pushing away the interstellar medium in all directions.

It's amazing that the bow shock for Alpha Cam is 10 light-years from the star, when our solar system's heliopause is just one light-day from our star.