Rogue Stars

[Ixion]

Ok, I have a question about astronomy (actually several questions). I read an article somewhere (maybe Space.com but I can't remember) that some stars within the galaxy get ejected into space from being slingshotted from massive black holes. The article implied that many of these stars are sent back into the plane of the galaxy because they were rotating within the axis of symmetry. However, also implied was that a few stars that got ejected were sent hurtling into open space between galaxies.

So my question is, does anyone have an idea how common these open-space rogue stars are? Can this even be approximated? Do you think it would be more common for stars to be ejected into space if the galaxy they originated from has a more three-dimensional structure, such as lenticular galaxies as opposed to barred or spiral galaxies? When they show stars from Hubble telescope and other deep space telescopes, my understanding is that the majority of those are from within the Milky Way Galaxy. Other pictures are simply of other galaxies or stars within other galaxies. Am I correct in this assumption?

I am not worried about collisions with other objects, as space is big and empty. My understanding is that these rogue stars would hurtle through space and continue the regular life cycle of a star, eventually burning out in the open. I am just curious about this phenomena but do not have enough astronomical knowledge to answer these questions.

[Arthur Denton]

Quoting from Space Daily:

Originally Posted by w w w .spacedaily.com/reports/Rogue_Star_Dangers_Thought_Slight.html

Rogue Star Dangers Thought Slight

The latest discovery brings the total number of known exiles to five.
by Staff Writers
Washington DC (SPX) Jan 31, 2006
Recent research showing there is a small population of hypervelocity stars streaking through the Milky Way doesn't mean there is much of a risk to humanity, either of a cataclysmic collision within the solar system or of significant gravitational disruptions.

"There are vast empty distances between stars, and so a close stellar encounter is very unlikely as a hypervelocity star travels out of the galaxy," said lead researcher Warren Brown, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Brown told SpaceDaily.com that tidal disruption also is unlikely, unless the encounter occurred at extremely close range, "because a hypervelocity star travels so quickly there would be very little time for the gravitational pull to disrupt any planets."

Using the Multiple-Mirror Telescope in Arizona, Brown and colleagues have spotted two such stars ¿ each about four times more massive than the Sun ¿ moving fast enough so the galaxy's gravitation cannot contain them. The first, in the direction of the constellation Ursa Major, is traveling out of the Milky Way at about 1.25 million miles per hour. It is located about 240,000 light-years from Earth. The second, in the direction of Cancer, is moving outward at 1.43 million miles per hour and is about 180,000 light-years away.

The HSCA team discovered the first stellar exile last year. A European group has identified two more, one of which might have originated in the Large Magellanic Cloud, which is adjacent to the Milky Way. The latest discovery brings the total number of known exiles to five.

"These stars form a new class of astronomical objects ¿ exiled stars leaving the galaxy," Brown said, adding that there may be 1,000 such stellar rogues speeding through the Milky Way, or about one star in 100 million. Despite the long odds of discovery, the team found their target by pre-selecting candidates spread over a large area of the sky.

Stars become exiles when their path takes them too close to the supermassive black hole that exists at the Milky Way's center. In general, exiled stars start out as part of binary systems. Just as engineers can boost the velocity of spacecraft by maneuvering them close to planets, these stars receive a huge gravitational kick from the black hole, enough to eject them completely from the galaxy, and to break the bond with their binary partner.

One intriguing prospect regarding galactic exiles is whether they are carrying any planets along with them. "It is possible that these stars have planetary systems," Brown said. "If planets do currently orbit the exiled stars, the planets' motion is relative to the stars and is unaffected by the extreme speeds of their parent stars."

He said the odds of planets are low, however. "We believe that ¿ the most likely time for a planet to be either disrupted or stripped from its parent star altogether is during the encounter with the massive black hole."

Regarding the possibility of a close encounter with a rogue star, Brown said although anything massive that passes near or within the orbits of the planets would disrupt our solar system, "lucky for us, a close encounter with even one of the galaxy's 100,000,000,000 stars is very unlikely. Roughly speaking, there is a 0.01 percent chance of finding a hypervelocity star within 1,000 light years of Earth at any given time."

In terms of their ultimate fate, Brown said hypervelocity stars are doomed to travel alone in the blackness of intergalactic space. "They are traveling at speeds well over twice that needed to escape the gravitational pull of our galaxy, and so will never return," he said. "The stars will shine normally until they end their lives as supernova."

I think, considering the amount of times we've been shot by asteroids, that having the solar system collapsed by a sun (yes, we'd collapse by gravity, maybe, before the heat effects would be felt) will be thousands of times harder, given the cheer number of asteroids and the few impacts. Of course, this is related to a human scale of time, not an universe scale of time. And if there was a sun heading toward our system, we'd have loads of years to actually do something before it came, cause unlike other celestial bodies, they shine and say "hello, peeps, I'm here", which is a really big relief.

The most interesting thing about this topic is that, while researching for a good article, I went to wikipedia, and all I could find is references to a star wars game, which means it is less important than bashing some with yoda and stuff. Pity

[Ixion]

Thanks for the article. I was never worried about the dangers of a rogue star smashing into the solar system because:
1) We would see it coming.
2) Space is BIG and the chances are very small.
3) Heat would be as big, if not bigger, factor as gravity.

Nevertheless, the article mentions that they have spotted several intergalactic stars. I wonder if they have made the telescope data public. I will have to Google it.

[tumnus]

Well extra-galactic stars are, extra-galactic, so not of any worry to us (although I remember a Larry Niven short story where they land on a planet round a protostar that is only passing through our galaxy. Its made of anti-matter)

But I believe that the stars themselves including the sun are bobbing about like particles in brownian motion. Its too slow too see of course, but we are moving nearer to some stars and farer from others all the time.

Instead of collapsing the solar system, a large object passing nearby might cause pertubations in the Oort cloud that could send thousands of comets into the inner solar system. People speculate that this may have happened a few times in the past and helped nudge along a couple of mass extinctions.

[fuelair]

http://www.amazon.com/ROGUE-STAR-Sta...8138276&sr=1-3

Pohl and Williamson

[DeiRenDopa]

Some resources:

APOD's Stars Without Galaxies

APOD's Streams of Stars in the Virgo Cluster of Galaxies

Sky Survey Unveils Star Cluster Shredded By The Milky Way - from SDSS

Stars getting booted out of a galaxy (or globular cluster) by close encounters of the black hole kind are rare, but over the life of a galaxy, there will be big mobs.

However, tidal stripping, shredding, and other general mayhem caused by galaxy collisions and close encounters will result in far more lonely hearts stars ....

[MrQhuest]

http://antwrp.gsfc.nasa.gov/apod/ap060108.html

Tadpole Galaxy

[Dancing David]

That would be wierd to look up at the night sky and see only the fuzzy blobs of galaxies. No real dreams of interstellar travel there.