APOD: Runaway Star Alpha Camelopardalis (2023 Apr 28)

[Ann]

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

---

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

---

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

---

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

---

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.

You may be right about Kappa Cas.

Phil Plait of Slate.com wrote:


Comment

Correction, March 6, 2014: Well, this will take a moment to explain.

In the article below, I wrote that the star Kappa Cas is moving through the galaxy at a stunning 1,100 km/sec. This turns out to be incorrect: The speed of the stellar wind blowing off its surface is that fast, but the star itself is moving far more slowly.

I based the original number off the NASA press release, which made that assumption about the speed. However, an email by astronomer Manfred Pakull set me straight. The star is actually moving relative to the Sun at about 25 km/sec, which means it’s moving around the galaxy at around the same speed we are.

So why is there an arc of material compressed next to it instead of a more spherical shell of dust? The speed of the star is very small compared to the wind speed, so I’m guessing the dusty material the star’s wind is ramming is not evenly distributed. Note that the overall shape is more like part of a sphere as opposed to a bow wave, so this seems likely. Funny, too: When I read the press release I looked for journal papers on the star and found none (Pakull did mention one, which has some relevant numbers for the star). That’s surprising if it really is a runaway star, so now that anomaly makes more sense. Everything else I wrote below is correct, but note that the parts about it being a runaway are almost certainly incorrect. And also? It’s still gorgeous.

Ann

[johnnydeep]

...
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.

It seems to be well established that Kapp Cass is a fast moving star that is causing the visible "bow shock wave". What makes a star a "runaway" other than speed relative to neighbors I'm not sure. Wikipedia has this to say:

It is a runaway star, moving at around 2.5 million mph relative to its neighbors (1,100 kilometers per second). Its magnetic field and wind of particles creates a visible bow shock 4 light-years ahead of it, colliding with the diffuse, and usually invisible, interstellar gas and dust. This is about the same distance that Earth is from Proxima Centauri, the nearest star to the Sun.[17] The dimensions of the bow shock are vast: around 12 light-years long and 1.8 light-years wide.[18]

See also https://www.jpl.nasa.gov/news/the-shock ... peedy-star

[ EDIT: well Ann beat me to what seems to be a conflicting measurement of Kappa Cass's speed. So perhaps it's not so much of a "runaway" after all? ]

[javachip3]

... 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...

Correction, 22600 years, at 25.7 trillion miles divided by 36 miles per second.