Page 1 of 1
APOD: The Antennae (2011 Apr 29)
Posted: Fri Apr 29, 2011 4:06 am
by APOD Robot
The Antennae
Explanation: Some 60 million light-years away in the southerly
constellation Corvus, two large galaxies
collided. But the stars in the two galaxies, cataloged as
NGC 4038 and NGC 4039, don't collide in the course of the
ponderous event, lasting hundreds of millions of years. Instead, their large clouds of
molecular gas and dust do, triggering furious episodes of star formation near the center of the
cosmic wreckage. Spanning about 500 thousand light-years,
this stunning view also reveals new star clusters and
matter flung far from the scene of the accident by
gravitational tidal forces.
Of course, the suggestive visual appearance of the extended arcing structures gives the galaxy pair its popular name - The Antennae.
[/b]
Re: APOD: The Antennae (2011 Apr 29)
Posted: Fri Apr 29, 2011 4:18 am
by bystander
Re: APOD: The Antennae (2011 Apr 29)
Posted: Fri Apr 29, 2011 12:57 pm
by grahamluckhurst
What would happen to planets around stars in colliding galaxies? Are they deep enough inside the star's gravity well or do some of them get cast out into the inter-galatic void?
Re: APOD: The Antennae (2011 Apr 29)
Posted: Fri Apr 29, 2011 1:28 pm
by Chris Peterson
grahamluckhurst wrote:What would happen to planets around stars in colliding galaxies? Are they deep enough inside the star's gravity well or do some of them get cast out into the inter-galatic void?
The majority would be unaffected. Only where the core regions are involved will stars get close enough together to produce serious perturbations at the planetary system scale. And it's likely that in core regions, stars are already too close together to allow for stable planets, even when galaxies aren't colliding.
Re: APOD: The Antennae (2011 Apr 29)
Posted: Sat Apr 30, 2011 7:47 pm
by grahamluckhurst
Thanks Chris, I feel much safer now.
Re: APOD: The Antennae (2011 Apr 29)
Posted: Sun May 01, 2011 10:18 pm
by kshiarella
Chris Peterson wrote:grahamluckhurst wrote:What would happen to planets around stars in colliding galaxies? Are they deep enough inside the star's gravity well or do some of them get cast out into the inter-galatic void?
The majority would be unaffected. Only where the core regions are involved will stars get close enough together to produce serious perturbations at the planetary system scale. And it's likely that in core regions, stars are already too close together to allow for stable planets, even when galaxies aren't colliding.
How close would two sun-sized stars have to be to de-stabilize a solar system? Are most binary systems unstable for planet formation or can such systems have planets with complex orbits around two self-orbiting stars? And at Galaxy and star cluster "cores" how closely are stars packed before they start falling into each other and making a black hole?
Re: APOD: The Antennae (2011 Apr 29)
Posted: Sun May 01, 2011 10:57 pm
by NoelC
Chris Peterson wrote:And it's likely that in core regions, stars are already too close together to allow for stable planets, even when galaxies aren't colliding.
Willing to discuss this statement further? How near the absolute core are we talking about?
It doesn't seem to me that stars being a few light years apart is enough to be a problem for planets. How is it, for example, that our own almost-star Jupiter has a nice set of satellites in perfectly good orbits? It's only a few light-
hours from the nearest star.
Are you proposing that the planets wouldn't form to begin with? I question even that (again using Jupiter as an example), but is there any reason to think that they couldn't have formed further out?
Just how close together do you think the stars are in the core of a galaxy?
-Noel
Re: APOD: The Antennae (2011 Apr 29)
Posted: Sun May 01, 2011 11:28 pm
by Chris Peterson
NoelC wrote:It doesn't seem to me that stars being a few light years apart is enough to be a problem for planets. How is it, for example, that our own almost-star Jupiter has a nice set of satellites in perfectly good orbits? It's only a few light-hours from the nearest star.
I've seen simulations that suggest that a single star passing within a few tenths of a light year of the Sun could destabilize the Solar System. The stellar density in the bulge of the Milky Way is between 1000 and 2000 stars per cubic light year. It is doubtful that stable planetary systems could exist in such a region. The situation in that environment is very different than what you have with Jupiter's system, which while chaotic, is essentially metastable. Unstable orbits have already been weeded out. But a planetary system in a dense galactic core sees a non-repeating set of gravitational perturbations. Essentially, every close encounter is a new event, introducing its own unique set of instabilities.
Are you proposing that the planets wouldn't form to begin with?
I'd expect planets to form in most star systems, including those in dense regions. Planetary system formation seems to be very quick- a few million years. Chaotic instabilities probably manifest over tens or hundreds of millions of years, so stars will tend to have all but very closely orbiting planets cleared out. At the least, planets will get shifted into different orbits, meaning that even where planets exist, they are almost certainly hostile to the development of life (or life requiring significant evolutionary time).