 Artist's concept of US 708 (the blue star on the left) | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 09h 33m 20.865s[1] |
| Declination | +44° 17′ 05.52″[1] |
| Apparent magnitude (V) | 18.8[1] |
| Characteristics | |
| Spectral type | sdOHe[1] |
| Astrometry | |
| Radial velocity (Rv) | 708.0 ± 15.0[2] km/s |
| Proper motion (μ) | RA: −7.33 ± 0.58[2]mas/yr Dec.: 2.28 ± 0.55[2]mas/yr |
| Distance | 60,300 ± 8,500 ly (18,500 ± 2,600[2] pc) |
| Details[2] | |
| Surface gravity (log g) | 5.23 ± 0.12 cgs |
| Temperature | 44561 ± 675 K |
| Other designations | |
| SDSS J093320.86+441705.4 | |
| Database references | |
| SIMBAD | data |
US 708 is ahyper-velocityclass O subdwarf inUrsa Major, in the halo of theMilky Way Galaxy. One of the fastest-moving stars in thegalaxy, the star was first surveyed in 1982.[3][4][5]
US 708 was first discovered in 1982 by Peter Usher and colleagues ofPennsylvania State University as a faint blue object in theMilky Way halo.Sloan Digital Sky Survey measured the star again in 2005.[6]
In 2015, Stephan Geier of theEuropean Southern Observatory led a team that reported inScience that the velocity of the star was 1,200 km/s (4,300,000 km/h; 2,700,000 mph), the highest ever recorded in the galaxy.[3][7][8] The star's high velocity was originally suspected to be caused by the massiveblack hole at the center of the galaxy. But now it is found out that the star must have crossed the galactic disk about 14 million years ago and thus it did not come from the center of the galaxy; hence the speed now possessed by the star may not be attributed to the black hole.[9]However, closer study suggested it had been one element of a pair of close binary stars.[10]
Its companion had already entered itswhite dwarf stage when US 708 entered itsred giant phase. Their respective orbits changed as its companion took gas from the outer layers of US 708. Then its companion acquired enough mass to gosupernova, which triggered US 708 being flung away at its high velocity, not by the black hole at the center of our galaxy.[11] The team behind the new observations suggests that it was orbiting a white dwarf roughly the mass of the Sun with an orbital period of less than 10 minutes.[7][8]
The star is a high speed rotating, densehelium star which is supposed to be formed by the interaction of a companion star nearby. These stars are composed of helium, which is the remnant of a massive star which had lost its envelope of hydrogen. Geier's team describe the star as the"fastest unbound star in the galaxy" and employed theEchellette Spectrograph and Imager attached to the 10 meterKeck II telescope inHawaii.[12] Its velocity exceeds theescape velocity of our galaxy.[13]
Hypervelocity stars (HVSs) travel with velocities so high that they exceed the escape velocity of the Galaxy.
Scientists using the W. M. Keck Observatory and Pan-STARRS1 telescopes on Hawaii have discovered a star that breaks the galactic speed record, traveling with a velocity of about 2.7 million mph (1,200 km/s). This velocity is so high, the star will escape the gravity of our galaxy. In contrast to the other known unbound stars, the team showed that this compact star was ejected from an extremely tight binary by a thermonuclear supernova explosion.
A multinational team of astronomers led by Dr Stephan Geier from the European Southern Observatory in Garching, Germany, has determined that a hypervelocity star known as US 708 is traveling at about 1,200 km per second.
By measuring the velocity, trajectory and rotation of the star, known as US 708, researchers at the European Southern Observatory determined that it started life as one half of a close binary pair — two stars that closely orbited one other.
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