#high proper motion

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Visiting a Star System from Andromeda

In an age where even thinking about visiting a star system outside of the Solar System, the idea that even if we surpassed this barrier, we'd ever come close to visiting a system from Andromeda may sound fairly wild, but astronomers from Karlsruhe Institute of Technology in Germany have postulated an interesting idea, what if the star's came to us ?

In our Milky Way there are many high proper motion stars, i've featured them on this blog many times, and most of the Ursa Major big dipper or frying pan are exactly these kind of stars, moving at a very different speed and direction than our star is orbiting our galaxy.

We've also known for a long time that some stars are moving so fast, often ejected by supernova or a close encounter with a black hole, that they could exit the Milky Way.

The team of astronomers have calculated the number of stars that could have migrated from Andromeda to the Milky Way, and have concluded that between 12 to 4000 of such stars may currently reside in our own area of the galaxy.

If this is true, then it's quite likely that Gaia may have already detected them, and the team plan to follow through the billions of stars it has already mapped to see if any have the tell tail direction and speed we'd expect.

It could be that a star not so far away (in local galaxy terms) is from Andromeda, and may have even brought it's planets for the ride, assuming they were already developed and survived the cataclysmic encounter to make the journey here.

Source:

The Milky Way could contain thousands of stars from another galaxy

We know there are stars moving fast enough to escape the Milky Way, so the same is probably true of other galaxies. Now, simulations suggest

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IC 405 - Flaming Star Nebula

1,500 light years from Earth in the Northern constellation of Auriga, this reflective (blue) and emissions (red) nebula holds some interesting secrets.

The proper motion (the direction of travel of the star) of the central star appears to lead back to the Orion Nebula.

More so, recent research on a white dwarf named J0927 has suggested it may be the fastest moving known star in our galaxy, moving at over 5 million miles per hour, enough to actually break through the galaxy gravity and spin off into intergalactic space.

For a while dwarf to have reached these speeds, it must have been ejected from a type 1a supernova, and a very special type at that.

Type 1a supernova's occur when a white dwarf gains mass, exceeds the Chandrashekar limit and goes supernova, normally from a close partner. In this instance it is thought two white dwarfs that had significant left overs of helium from their former red giant stars got too close and the helium accreted to one and cause the white dwarf to re-animate itself, in what is known as a dynamically driven double-degenerate double-detonation (D6) supernova.

Many stars in our night sky have high proper-motions, although most is because their orbit around our galaxy differs significantly from ours, but these few examples of stars with hypervelocity make you understand that intergalactic space is probably full of stars, many speeding away from their galaxy of origin, some that may even get captured by our Milky Way, even if they are white dwarfs.

Source :

Scientists discover the fastest stars ever seen in the Milky Way

Astronomers discovered a new population of ultra-fast-moving stars, including the fastest 'runaway' star ever seen in our galaxy.

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Orphaned Stars

While it's not impossible for a star to be born outside of a galaxy, the conditions needed for star formation are very much more common within one, in that you need a body of dense cold hydrogen, and it's the gravitational attraction of a galaxy that brings it all together in a single place, and holds it together.

Almost all stars start life in a galaxy, they can find themselves flung out into the space between galaxies, most commonly from mergers, although in some instances from nearby supernova that can literally fling the star out.

Our own sky has many examples of stars with what we call High Proper Motions (such as Barnard's star), stars that don't follow the normal orbit around the galaxy, but while this is a very small number, the majority of them will retain their orbit in our galaxy, despite the odd orbit. Such stars appear to move over time in our night sky, while the others that follow us around, appear almost stable.

(above, Barnard's Star's movement over 20 years)

An orphaned star won't necessarily lose it's planets, and so, it's possible that life could exist orbiting a star that has no home galaxy, a dark sky with almost little visible.

I find it intriguing to imagine such a species inventing optics for ground base use, and then one day somebody thinks to look up and spots the faint blur's of galaxies around them, although of course, the planets in their system would be visible, just as ours are.

And then 3-5 Billion years into our own future, we too will face the possibility of our own star being thrown out. It's impossible to know for sure how the merger between Andromeda and the Milky Way will play out, if the remnants of our own Sun will be flung afar, or end up at the newly formed core of a massive elliptical galaxy, but the fate we see of other galaxies, is coming our way too !

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The Supernova Canon and the Pulsar Cannonball

Our human lives are so short, we tend to look up and the never changing stars in the night sky and see it as eternal, but there's monsters beyond most of our imaginations out there, monsters of physics of course, but one interesting one is captured in the image above, derived from radio waves and infra red observatories, a supernova remnant and something shooting out of it, in this instance, a Pulsar ! The remnant of a once large star that collapsed after fusion ended and gravity crushed back turning the entire object into a ball of neutrons little larger than a big city, but maintaining the gravity of 2 or more times that of our Sun.

Somehow this supernova ended up firing out the Pulsar into the Milky Way with enough energy it's quite likely it will leave the Milky Way altogether.

The supernova remnant now known as the Medulla Nebula (known also as CTB-1) is located in the constellation of Cassiopeia

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The Seagull Nebula

3,650 light years in the constellation of Monoceros, bordering Canis Major and not so far from Sirius (the brightest star in the sky) lies the emissions and reflection nebula known as the Seagull or IC 2177.

Of particular interest is the star FN Canis Major, a high proper motion star which displays a bow shock wave in the nebula.

The star is thought to have been ejected from the OB Association (a cluster of very large blue giant stars) and is part of a binary system of which the most significant star appears to be moving off the main sequence towards the red giant phase of its life.

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The "Peekaboo Galaxy"

Until recently this distant dwarf galaxy was impossible for us to see, not because we didn't have telescopes that could have seen it but because the bright star appearing next to it was concealing it.

As you'll be aware, our Sun is moving around the Galaxy every 230 million years or so, as do most other stars in our nights sky, but not every star follows the same path, and can appear to be moving much faster from our perspective. The star next to the galaxy was one of these high proper-motion stars, and over the last 50-100 years has slowly moved away revealing behind it a galaxy, and hence the name "Peekaboo".

The dwarf galaxy appears to be 20 million light years from Earth in the constellation of Hydra, and has got scientists excited due to it's chemical make up, having a very metal poor environment similar to what is expected at the start of the universe. In astronomy Metals are any element above Helium, so when we say Metal Poor, we mean it's Hydrogen and Helium almost exclusively.

The puzzle here is, this galaxy doesn't appear to have any old population stars, with the oldest around 2 billion years old (our own Star is almost 5 billion) and you'd really expect to see more metals in such stars.

Source:

https://www.universetoday.com/159045/a-star-was-blocking-a-galaxy-but-now-its-moved-enough-that-astronomers-can-finally-examine-what-it-was-hiding/

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Galactic Shooting Stars

You may be familiar with shooting stars, even seen some, but what you're seeing are not stars at all, but rather, tiny specs of dust entering the Earth's atmosphere as it orbits the Sun.

There's a totally different kind of shooting star, that really are stars ! They are known as High Proper Motion stars, and while the lifespan of us humans doesn't allow us to see them in their true glory, on a galactic scale, they are screaming around our galaxy, often in bizarre irregular orbits.

Our sun orbits the Milky Way, it takes about 250 million years to do so, and almost all the stars in our galaxy follow suite. While this is the case, most stars follow a fairly similar pattern around the galaxy, with enough deviation to make different stars come closer and further over time, depending on their speed and trajectory. All of these stars are being mapped by Gaia which has produced a map of the galaxy showing the movement of the stars.

Now you'll notice there's a fair few that aren't following the same path, not just that, they are travelling 10 to 100 times faster than the other stars in our galaxy, the suspicion for some time has been, these high proper motion stars are "not from round these parts !" .. ie .. Intergalactic in nature, having at some point been caught by the gravity of our galaxy.

Researchers at the Carnegie Institution for Science in California have mapped a group of the fastest moving stars in our galaxy, and looked at the metallicity and chemical composition of these stars, and found in almost every case, the chemicals found in these stars didn't match the average expectation for the same type of star in our Milky Way.

This could indicate an extra galactic origin, however, stars are creatures of the nebula they are born in, and the Milky Way will have had billions of such areas forming stars over the last 10 billion years, so it cannot be ruled out that they were just formed in a unique environment within the Milky Way quite yet.

There's been numerous galaxy mergers with our own galaxy over the billions of years of history, so that entire groups of stars follow their own rules, isn't so much a surprise, and this study is another indicator of this being the probable cause for them.

Source : https://www.newscientist.com/article/2315487-some-of-the-fastest-stars-in-the-milky-way-come-from-other-galaxies/?utm_source=onesignal&utm_medium=push&utm_campaign=2022-04-10-Fast-stars