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Fraser
2005-Nov-09, 05:51 PM
SUMMARY: Astronomers have discovered a massive star moving extremely quickly through the outer halo of the Milky Way, and into intergalactic space. The star, named HE 0437-5439, was discovered as part of the Hamburg/ESO sky survey, and was clocked traveling at 723 km/s, or 2.6 million kilometres per hour (1.6 million miles an hour). It's possible that the star was accelerated when it came too close to a supermassive black hole in the centre of the Large Magellanic Cloud.

View full article (http://www.universetoday.com/am/publish/star_on_the_run.html)
What do you think about this story? post your comments below.

iantresman
2005-Nov-10, 12:46 PM
The press release says "Either the star is older than it appears or it was born and accelerated elsewhere."

If the star was born and accelerated elsewhere, then a supermassive black hole did not accelerate it, in which case we must look at alternative mechanisms for accelerating a ball of plasma?

I wonder if the star has a plasma tail, or whether its speed is changing.

Regards,
Ian Tresman

GOURDHEAD
2005-Nov-10, 03:48 PM
Is there some reason that slingshoting was not mentioned except in the context of the binary case where one star is swallowed by a black hole. Then there is the case where critters with advanced technological development could be driving it where they wish it to go taking their planet (which they would have had to attach or build there if the age estimate is correct) along by gravitational coupling. Perhaps we have discovered them at last. Wish Fermi were here to enjoy.

Back to slingshoting, when a single star is accelerated by passing near a black hole, energy is taken from the balck hole to accelerate the star. How does the black hole give up this energy? Loss of spin rate? Photons escaping momentarily due to the assist from the gravitational pull of the passing star? Alteration of the Lens-Thirring effect? Other? All of the above and more?

If such a star should draw near a binary set of rather large (massive) black holes of approximately equal mass orbiting each other just outside the range of mutual absorption, is there a trajectory available to it that would cause it to be accelerated to the observed velocity by the slingshot effect? Would this scenario, with the black holes only, tend to cause each of them to explode violently by tearing each other apart? Could the close passing of this star trigger the event?

Gerald Lukaniuk
2005-Nov-11, 06:02 AM
Perhaps we are looking down the business end

of a massive propulsion system giving us a

false impression through deductions assuming

it is a star. Gravitional slingshot

simularions and our experiences with probes

such as voyager are based on solid elastic

objects. As gourd head suggested a tug

intense enough to slighshot such as gaseous

object would likely rip it apart if it was

totALLY gaseous or strip it of its plasma and

hence its glow if it has an iron or neutron

core. Hopefully someone will do the math

exploring the possibity that it is an unknown

technology as perhaps clues in its behavior my

accelerate or own efforts to escape the red

neck morons running this planet.

LurchGS
2005-Nov-12, 06:45 AM
At risk of being flip, I'd say it's the Puppeteers..

Iantresman - I'm not following your assertion that if the star were born and accelerated elsewhere, there could be no supermassive black hole involved. As I read the article, it states pretty plainly that this star's vector would give credence to any suggestion that the SMC does indeed have such a mass at its center.

Gourdhead - I admit I'm no astronomer/cosmologist - but everything I've seen indicates to me that black holes do not explode. period. If they get too close, they merge. Probably not without a lot of nasty radiation flung about, true, but I believe that would be the result of the accretion disks getting all confused...

Gerald - I think it would be - at best- difficult for a *single* stellar object to survive a slingshot trajectory that would result in this vector. But if a binary system approached a SMBH, then I'd be much more inclined to think it possible. It would depend on point of closest approach, I'd think. There was probably some damage and deformation to the star when it happened, but that was millions of years ago - it's long since recovered to its base spheroid shape

---------------

why do they call it a gravity well? Well.... it's like this...

iantresman
2005-Nov-12, 04:51 PM
Iantresman - I'm not following your assertion that if the star were born and accelerated elsewhere, there could be no supermassive black hole involved. As I read the article, it states pretty plainly that this star's vector would give credence to any suggestion that the SMC does indeed have such a mass at its center.

I assumed that if there was a supermassive black hole involved, then it could only be located in the centre of the galaxy on the grounds that anywhere else would have some kind of signature. I suppose it could be outside of the galaxy, but I can't see any reason for it to be there.

That's why assumed that the authors had suggested the two possible scenarious.

Regards,
Ian Tresman

jimmarsen
2005-Nov-12, 10:43 PM
The reports I've been able to find all seem to be a rehash of the ESO press release. They are unclear on how the HE 0437-5439's distance (200,000 light years) and recession velocity (723 km/s) were calculated.

If the recession velocity was derived from its redshift, I calculate it would be 13 times farther away than the Andromeda galaxy according to the Hubble relation (z=.0023, r = 33 million light years for H0=71).

If the object does have a redshift of z =.0023, how do astronomers decide whether the redshift is due to the Doppler effect (and therefore does not equate to distance) or cosmological (and the Hubble relation implies distance)? Is there a minimum value for applying the Hubble relation?

For example, Ton 202 was originally listed as a faint blue star with a measurable proper motion (53 mas/yr) (Luyten 1969) until its redshift was measured at z=.366 and it was reclassified as a quasar (see http://www.aas.org/publications/baas/v31n3/aas194/267.htm).

RussT
2005-Nov-13, 02:40 AM
I have seen several abstracts indicating some size massive black holes in dwarf galaxies, but since the don't appear to be 'massive' enough, or maybe they don't 'spin' strongly enough, they don't appear to be causing an AGN to form and make them 'small' spiral galaxies.

Any other thoughts on this?

RussT

GOURDHEAD
2005-Nov-14, 04:21 PM
Gourdhead - I admit I'm no astronomer/cosmologist - but everything I've seen indicates to me that black holes do not explode, period. If they get too close, they merge.I'm not either but, although the most likely result is a merger, can we be sure there is no set of conditions that would cause mutual ripping apart? May there be within the event horizon things with kinetic energies just below the escape threshold that each black hole can rip from the other leading to a feed back loop that completely unravels each within a few days. My!! such a sight to behold!!....from whatever a safe distance is, if there is one, of course.

RussT
2005-Nov-14, 11:30 PM
I still would appreciate some feedback on 'medium' size black holes in dwarfs!

But, what if...the magnetic charge (field) on the outside of black holes are just like 'Magnets'...where trying to touch the same polls make them repel each other?

Have we ever seen or measured 2 black holes in close proximity to determine their motions in this way?

RussT
S=G

Tim Thompson
2005-Nov-17, 02:50 AM
The paper has been accepted by the Astrophysical Journal Letters, and is available as a preprint: HE 0437-5439: An Unbound Hypervelocity Main-Sequence B-Type Star (http://cul.arxiv.org/abs/astro-ph/0511321).


Abstract: We report the discovery of a 16th magnitude star, HE 0437-5439, with a heliocentric radial velocity of +723 3 km s-1. A quantitative spectral analysis of high-resolution optical spectra obtained with the VLT (http://www.eso.org/outreach/ut1fl/) and UVES (http://www.eso.org/instruments/uves/) shows that HE 0437-5439 is a main-sequence B-type star with Teff = 20,350 K, log g = 3.77, a solar (within a factor of a few) helium abundance and metal content, and rotating at v sin i = 54 km s-1. Using appropriate evolutionary tracks, we derive a mass of 8 Msolar and a corresponding distance of 61 kpc. Its Galactic rest-frame velocity is at least 563 km s-1, almost twice the local Galactic escape velocity, indicating that the star is unbound to the Galaxy. Numerical kinematical experiments are carried out to constrain its place of birth. It has been suggested that such hypervelocity stars can be formed by the tidal disruption of a binary through interaction with the supermassive black hole at the Galactic center (GC). HE 0437-5439 needs about 100 Myr to travel from the GC to its present position, much longer than its main-sequence lifetime of 25 Myr. This can only be reconciled if HE 0437-5439 is a blue straggler star. In this case, the predicted proper motion is so small that it can only be measured by future space missions. Since the star is much closer to the Large Magellanic Cloud (http://www.seds.org/messier/xtra/ngc/lmc.html) (LMC; 18 kpc) than to the GC, it can reach its position from the center of the LMC. The proper motion predicted in this case is about 2 mas yr-1 (relative to the LMC), large enough to be measurable with conventional techniques from the ground. The LMC origin could also be tested by a high-precision abundance analysis.

Note that the velocity measured is "radial", meaning that it is along the line of sight. The proper motion, perpendicular to the line of sight, has not been measured.

John Kierein
2005-Nov-17, 10:32 PM
I suspect this is an ordinary stationary star with a non-doppler red shift. An intinsic red shift such as is seen on the sun.
http://tinyurl.com/8ws3z

LurchGS
2005-Nov-24, 05:33 AM
I'm not either but, although the most likely result is a merger, can we be sure there is no set of conditions that would cause mutual ripping apart? May there be within the event horizon things with kinetic energies just below the escape threshold that each black hole can rip from the other leading to a feed back loop that completely unravels each within a few days. My!! such a sight to behold!!....from whatever a safe distance is, if there is one, of course.

Again - I have no idea on the math - but one of the primary properties of a black hole is that *nothing* can escape from within the event horizon. At a guess, if two black holes were in close enough proximity to seriously affect each other, I would guess that the event horizons might distort eliptically toward the other hole, but still, nothing would come *out*.
And, of course there would be all kinds of fireworks from the interaction of the accretion disks and other external material

Blob
2006-Jul-21, 10:21 AM
Title: Ejection of Hyper-Velocity Stars from the Galactic Centre by Intermediate-Mass Black Holes
Authors: Holger Baumgardt, Alessia Gualandris, Simon Portegies Zwart

Researchers have performed N-body simulations of the formation of hyper-velocity stars (HVS) in the centre of the Milky Way due to inspiralling intermediate-mass black holes (IMBHs). They considered IMBHs of different masses, all starting from circular orbits at an initial distance of 0.1 pc.
The researchers find that the IMBHs sink to the centre of the Galaxy due to dynamical friction, where they deplete the central cusp of stars. Some of these stars become HVS and are ejected with velocities sufficiently high to escape the Galaxy. Since the HVS carry with them information about their origin, in particular in the moment of ejection, the velocity distribution and the direction in which they escape the Galaxy, detecting a population of HVS will provide insight in the ejection processes and could therefore provide indirect evidence for the existence of IMBHs.
Their simulations show that HVS are generated in short bursts which last only a few Million yars until the IMBH is swallowed by the supermassive black hole (SMBH). HVS are ejected almost isotropically, which makes IMBH induced ejections hard to distinguish from ejections due to encounters of stellar binaries with a SMBH. After the HVS have reached the galactic halo, their escape velocities correlate with the distance from the Galactic centre in the sense that the fastest HVS can be found furthest away from the centre. The velocity distribution of HVS generated by inspiralling IMBHs is also nearly independent of the mass of the IMBH and can be quite distinct from one generated by binary encounters.
Finally, their simulations show that the presence of an IMBH in the Galactic centre changes the stellar density distribution inside r<0.02 pc into a core profile, which takes at least 100 million years to replenish.

Read more (http://arxiv.org/PS_cache/astro-ph/pdf/0607/0607455.pdf) (124kb, PDF)

See also:
Title: A Successful Targeted Search for Hypervelocity Stars
Authors: Warren R. Brown, Margaret J. Geller, Scott J.Kenyon, Michael J. Kurtz (Smithsonian Astrophysical Observatory)

Hypervelocity stars (HVSs) travel with velocities so extreme that dynamical ejection from a massive black hole is their only suggested origin. Following our discovery of the first HVS, we have undertaken a dedicated survey for more HVSs in the Galactic halo and present here the resulting discovery of two new HVSs: SDSS J091301.0+305120 and SDSS J091759.5+672238, travelling with Galactic rest-frame velocities at least +558+-12 and +638+-12 km/s, respectively.

http://static.flickr.com/21/91623135_ca6bcd5d21_o.gif

Read more (http://arxiv.org/PS_cache/astro-ph/pdf/0601/0601580.pdf) (PDF)


Title: The Hypervelocity Star SDSS J090745.0+024507 is a Short-Period Variable
Authors: Cesar I. Fuentes, K. Z. Stanek, B. Scott Gaudi, Brian A. McLeod,
Slavko B. Bogdanov, Joel D. Hartman, Ryan C. Hickox, Matthew J. Holman

Researchers have taken high-precision photometry of the hypervelocity star SDSS J090745.0+024507 (HVS), which has a velocity of v=709 km/s, and is on course to leave our galaxy. It has likely been ejected from the supermassive black hole in the Galactic centre.

Read More (http://arxiv.org/PS_cache/astro-ph/pdf/0507/0507520.pdf) (PDF , 80kb)


And see also http://www.bautforum.com/showthread.php?t=26436