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How high-speed stars avoid the galaxy



To B or not to B

To date, almost all known hypervelstar stars are B-type sols in the main sequence, the period of their lives when they produce energy by melting hydrogen to helium in the nucleus. Because such stars live no more than several hundred million years, you wouldn't want to find someone on the galaxy's edge.

"These B-stars shouldn't exist there," says Brown. "There is no star formation in the outer Melkvägshaloen. It is a dead region – the galaxy halo contains the galaxy's globular clusters and old, metal-poor, low-mass stars. If it did not, you would never expect to see a B-star traveling at these speeds in the outer halogen. "

But there they are. The best explanation for their existence is a binary star that dares to close a massive black hole, says Hagai Perets, an astrophysicist at the Technion-Israel Institute of Technology in Haifa. The black hole captures a star in a very eccentric orbit and ejects the other as a hypervelocity star.

A decade after Brown and his colleagues discovered the first star, there is still a lack of data on bona fide hypervelocity stars across the sky. Astronomers can measure the radial velocity of any given star by examining its spectrum ̵

1; light is scattered in its input wavelengths. If an object moves towards us, its spectral lines shift to shorter wavelengths; If it moves away, the lines will turn to longer wavelengths. The higher the speed, the greater the shift.

Although this type of spectral analysis is simple for nearby stars, it becomes much more difficult for distant suns in the outer halo of the Milky Way. Even large telescopes cannot gather enough light. Therefore, astronomer Ulrich Heber at the University of Erlangen-Nuremberg in Germany believes that there are probably several low-mass hypervelocity stars waiting to be discovered. Although these design objects live longer than their B-type cousins, they radiate much less light and so they cannot be seen as far away. Still, they would be easier to spot than the smoother white dwarf residues of any dead B-type star.



Theologian Los Hills, Hills Hills, predicted hypervelocity stars in 1988, but astronomers did not find one until 2005.


On the way

When astronomers know of a star's radial velocity seen from Earth, they can calculate how fast it is moves in relation to the center of the galaxy. But this too only tells half of the story. To directly connect a passive star on the outer edge of the galaxy to its theoretical point of origin at the supermassive black hole in the Milky Way is the core, observers must also determine the star's movement over our point of view. This so-called movement is even more difficult to measure exactly than radial speed.

Astronomers determine the correct movement by observing the shift in the position of an object relative to more distant objects. For a hyper-loading star, this means measuring its motion in relation to background galaxies or quasars, a process that takes years.

Despite their collision speeds, hyperstyling stars have decent movements of less than 1 billion a year. (A millisecond second is equal to 0.000000005 ° or the angular size of a dime viewed from about 2,300 miles away.)

Soil-based studies are accurate to only about 5 billion seconds per year, so proper movement of hypervelstar stars must be done from space . This is where the European Space Agency's (ESA) Gaia mission comes in. This astronomical observatory – designed to measure precise positions and radial speeds of about 1 billion stars – provides true movement that is accurate to within 0.1 billion a year. In the next year or two, Gaia should offer amazing real moves for famous hypervel stars and new candidates.

These observations theoretically help to determine much more about the origins of these stars. Although scientists believe that most of them originate in interactions with Sagittarius A *, they still discuss whether some may be interlopers from outside the galaxy. Perhaps they went into the Milk's outer halo in a stream of stars from an early-disturbed dwarf galaxy. Or maybe the Milky Way satellite galaxy, Large Magellanic Cloud (LMC), radiated some in our galaxy halo.

"There is an unbound B-star, HE 0437-5439, which is close to the Great Magellanic Cloud which can either be from the LMC or the Milky Way," says Brown. "HE 0437-5439 moves away from us, and we do not know if it is angled on the road or to the LMC. "If this star came from the LMC, it could be the smoking service of a previously undiscovered mass of black holes that ejected the star at hypervelocity.


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