Our Sun May Have Migrated Over Time
Written by Nancy Atkinson
Computer simulation showing the development and evolution of the disk of a galaxy such as the Milky Way. Credit: Rok Roškar
When you stir cream in your coffee or tea, does the swirl stay the same or does it change as it spins in your cup? As galaxies form and swirl, the motions and eddies may actually cause stars to move within the galaxy. A long-standing scientific belief holds that stars tend to hang out in the same general part of a galaxy where they originally formed. But some astrophysicists have recently questioned whether that is true, and now new simulations show that, at least in galaxies similar to our own Milky Way, stars such as the sun can migrate great distances. If this is true, it could change the entire notion that there are parts of galaxies – so-called habitable zones – that are more conducive to supporting life than other areas.
"Our view of the extent of the habitable zone is based in part on the idea that certain chemical elements necessary for life are available in some parts of a galaxy's disk but not others," said Rok Roškar, a doctoral student in astronomy at the University of Washington. "If stars migrate, then that zone can't be a stationary place."
Roškar is lead author of a paper describing the findings from the simulations, published in the Sept. 10 edition of the Astrophysical Journal Letters. If the idea of habitable zone doesn't hold up, it would change scientists' understanding of just where, and how, life could evolve in a galaxy, he said.
Using more than 100,000 hours of computer time on a UW computer cluster and a supercomputer at the University of Texas, the scientists ran simulations of the formation and evolution of a galaxy disk from material that had swirled together 4 billion years after the big bang. Watch a simulation video.
The simulations begin with conditions about 9 billion years ago, after material for the disk of our galaxy had largely come together but the actual disk formation had not yet started. The scientists set basic parameters to mimic the development of the Milky Way to that point, but then let the simulated galaxy evolve on its own.
If a star, during its orbit around the center of the galaxy, is intercepted by a spiral arm of the galaxy, scientists previously assumed the star's orbit would become more erratic in the same way that a car's wheel might become wobbly after it hits a pothole.
However, in the new simulations the orbits of some stars might get larger or smaller but still remain very circular after hitting the massive spiral wave. Our sun has a nearly circular orbit, so the findings mean that when it formed 4.59 billion years ago (about 50 million years before the Earth), it could have been either nearer to or farther from the center of the galaxy, rather than halfway toward the outer edge where it is now.
Migrating stars also help explain a long-standing problem in the chemical mix of stars in the neighborhood of our solar system, which has long been known to be more mixed and diluted than would be expected if stars spent their entire lives where they were born. By bringing in stars from very different starting locations, the sun's neighborhood has become a more diverse and interesting place, the researchers said.
The findings are based on a few runs of the simulations, but the scientists plan to run a range of simulations with varying physical properties to generate different kinds of galactic disks, and then determine whether stars show similar ability to migrate large distances within different types of disk galaxies.
Source: University of Washington
Filed under: galaxies
September 16th, 2008 at 8:16 am
Could a star then migrate from Andromeda to the MIlky Way.?
September 16th, 2008 at 8:42 am
That would require divine intervention;)
September 16th, 2008 at 9:19 am
Maybe if a star was a runaway star (You can go look that up), which then got ejected out of the andromeda towards the Milky Way in a sprialing ecliptic path, which over time would allow the star the become a member of the Milky Way.
Of course you would have to do the maths and run supercomputer sims and possibly get observation evidence to back that up, but just maybe.
September 16th, 2008 at 1:53 pm
As recent work shows that the Andromeda and Milky Way galaxies are thought to be in a close flyby and eventual merger in from the next 5 to 10 billion years, stellar exchanges are likely to happen in the future. After the merger most of the stars from the ex-components of the two galaxies will be part of the merged structure - apart from those which have been ejected in the multiple close passes before the merger. So the only point at issue is do you mean in the present or past galactic eras?
September 16th, 2008 at 1:54 pm
Unfortunately, just like the notion that this solar system (or others) might capture 'runaway planerts' from elsewhere, it's hard to get a scenario that gets a signifigant ejection velocity, but also allows capture somewhere else.
And you'd surely end up with a highly elliptical orbit (of a runaway planet, and probably a runaway extragalactic star within this galaxy) if you did.
Oh, and it wouild be an insanely long cruise from Andromeda. It's (curently, as M31 is slowly approaching the Milky Way) a two million year trip, even at the speed of light. I have to think a runaway star isn't going to be going much above galactic escape velocity (which, I've read, is about 300,000mph for the Milky Way, and Andromeda may be more massive).
I'm not sure the Universe is even old enough to manage this.
September 16th, 2008 at 6:23 pm
Fascinating article - and it is hard to gauge what the ramifications may be for the development of life in a galaxy. On the one hand, this mixing and migration could mean that that much more of a galaxy is potentially habitable than one would tend to think, with life being able to arise and thrive in vastly different and diverse locations. This could mean life is relatively more common than one may imagine.
On the other hand, this finding may mean that the right combination of ingredients and conditions required for life to arise may be be transitory and fleeting - a star would need to be in just the right places at the right times for life to arise and evolve. If this is the case, life may be rare indeed.
Some great food for thought there…
September 17th, 2008 at 3:38 am
The Milky Way's escape velocity is roughly 335 km/s at 300,000 ly from the centre - the halo mass is a lot bigger than the disk mass. That speed is about 750,000 mph for all you Yanks. As the Sun is already doing 225 km/s I guess the needed boost isn't too onerous if the Sun did a stellar flyby with a compact object.
September 17th, 2008 at 4:34 am
This has been a standing theory for quite some time for many scientists. This is initially realized by noticing stars in 'arms' while gas and dust is just "all over". The would at least have to have some lateral movement for them to be somewhat aligned latterally. Also, stars on the outter fringes of many galaxies are not greatly affected by the gravity of the SMBH, yet somehow have gained the inertia to maintain orbit. More than likely, many of these systems or their origins were closer to the center of the galaxy. After suring up the latest theory on galaxy creation, the data more correctly reflects this.
Since we already know stars can be ejected from the galaxy, it is highly plausible planets could meet the same fate. This would normally occur when a star is gravitationally drawn towards the super massive black hole in the center of a galaxy, and has the wrong trajectory to enter orbit; instead of settling into a highly eliptical orbit it is thrown out of the galaxy; think of something along the lines of a gravitational assist on a massive scale. However, make it to another galaxy… I suppose its possible if they were close, but the probability would be waaay up there!
September 18th, 2008 at 12:18 am
I'm interested that many postnigs here refer to the capture/migration of stars outside of our galaxy, yet the article talks of the simulation for stars only within one such as the Milky Way.
Still an interesting article & if this is picked up & followed by other scientists, another potential building block of knowledge
September 18th, 2008 at 6:37 am
Hmm . . . I suspect that all stars, without exception, have migrated from their birthing place in the home galaxy. Angular momentum and centrifugal force suggests so. Considering the chaos we are witness to in the observable universe, it appears highly unlikely that the chemical elements supporting life having NOT been churned up within galaxies to where our interpretation of a "habitable zone" would be affected. On the other hand, Roskar could be right on target. Very interesting!