Departing at 723 km per second

glenc (Glen) · #1 21-08-2010, 04:40 PM

this is from S&T
A Runaway Star with a Story To Tell
Just five years ago the first hypervelocity star was confirmed, by Warren Brown of the Harvard-Smithsonian Center for Astrophysics. Now about 16 are known. These are stars moving through space so fast, upwards of several hundred kilometers per second, that they will escape the Milky Way's gravity and forever roam the intergalactic void. Their discovery had to wait for very efficient surveys; only about one in 100 million stars is going so fast.
Several possible mechanisms can fling a star with that much speed. But the most productive of them seems to be happening at a single, very special place. If a binary star falls close enough to the supermassive black hole at the Milky Way's center, the binary can be disrupted in such a way that one star is trapped around (or in) the hole and the other is slung away with preternatural velocity. This is thought to account for most of the escaping 16.
http://www.skyandtelescope.com/news/100993774.html

CraigS · #2 21-08-2010, 06:42 PM

Interesting ...

"The first hypervelocity star was confirmed 5 years ago.
They have now detected 16.
According to current surveys only about 1 in 100 million stars is going so fast".

I'm actually surprised they are so infrequent, taking into account what must be going on in/around the accretion disc of a galactic core.

I'll take a punt and guess there's a lot more out there than 1 in 100 million !
As they say, perhaps they're lurking around the core and we just can't see them coming yet. Or, maybe they die before we can see them, how do they effect the matter and space they encounter in their travels ?

Interesting.

Cheers

renormalised (Carl) · #3 22-08-2010, 12:39 PM

There's a few hypervelocity stars about, not all of them come from the galactic core....some are the results of supernova explosions and gravitational slingshots from other binary star interactions.

CraigS · #4 22-08-2010, 07:57 PM

Yep.
Paper says:

"We estimate the likelihood of HVS3 being a (former) binary by looking at the complete survey of Brown et al. (2007b), who infer 96±20 3-4 M⊙ HVSs are located within 100 kpc of the Galactic center."

...(perhaps .... they do say "infer")... and then ...

"At least 14 unbound stars have now been discovered in a targeted survey for HVSs (Brown et al. 2006a,b, 2007a,b, 2009) and another 3-5 unbound stars discovered in other surveys (Edelmann et al. 2005; Hirsch et al. 2005; Heber et al. 2008; Tillich et al. 2009; Irrgang et al. 2010). Unlike high proper-motion pulsars, which are the remnants of supernova explosions, known HVSs are mostly B-type main-sequence stars (Fuentes et al. 2006; Bonanos et al. 2008; L ́opez-Morales & Bonanos 2008; Przybilla et al. 2008a,b)."
?
Article says:
"The team is now trying to determine the origins of four other hypervelocity stars on the fringes of the Milky Way. "We are targeting [other] massive B stars," says Brown."

? .. help ..! .. can massive B-types also come from supernovas? (My lack of star origins knowledge, showing here).

Appreciate comments.

Cheers
PS: Wiki says: fast neutron stars (from supernovas) don't have the HVS ejection mechanism. (?). Galaxy 'mergers' seems to be one belief. Currently believed to originate by close encounters of binary stars with the supermassive black hole in the centre of the Milky Way (& other galaxy cores).

renormalised (Carl) · #5 23-08-2010, 09:58 AM

The massive B stars don't come from supernovae, they're the progenitors of the supernovae. Fast neutron stars are usually formed in the supernova explosion events. What happens is that you get an asymmetric explosion and the neutron star that usually forms in the core collapse gets shot out like a bullet out of a rifle.

CraigS · #6 23-08-2010, 10:19 AM

Ok. Got it. Thanks, Carl. Looks like the discrepancies may be just minor wording/terminology issues.

Looks like "RX J0822-4300, often referred to as a "Cosmic Cannonball"
... is unique in the apparent origin of its speed ..."
"Current theories fail to explain how such speeds can be attained from a supernova explosion. It could be a possible quark star."

Seems they are still defining the term HVS. Sometimes says "fast neutron stars (from supernovas) don't have the HVS ejection mechanism".

The fast neutron may end up with the label "quark star" .. a hypothetical exotic star with its own 'ejection mechanism. There's only one anyway (so far) ..

Thanks for the help.

Cheers

renormalised (Carl) · #7 23-08-2010, 10:25 AM

Looks like they're trying to separate an ejection mechanism derived from an explosive event from one that is purely gravitational, as it would be where a binary system was upset by a close encounter with the supermassive hole in Sag A*.

A quark star or neutron star would be ejected from a supernova explosion in exactly the same way, unless there was some weird reaction between the formation of the quark star and the surrounding debris from the explosion (or the explosion itself).

CraigS · #8 23-08-2010, 10:34 AM

Interesting ... it all leads back to the same thingy ...
"Quark matter may be one candidate for Dark Matter".

Man, this one's really pushing the limits, though ...
"Strange Quark Nuggets" .. available from all McDonalds' Restaurants after 10am !!