US 708
{{short description|Hypervelocity O-type subdwarf in the halo of the Milky Way Galaxy}}
{{Starbox begin |
name=US 708}}
{{Starbox image
|image=260px
|caption=Artist's concept of US 708 (the blue star on the left)
}}
{{Starbox observe
|epoch=J2000
|ra={{RA|09|33|20.865}}{{cite simbad
| title = US 708
| access-date = 28 November 2016 }}
|constell=Ursa Major }}
{{Starbox character
{{Starbox astrometry
|dist_ly=60,300 ± 8,500
|absmag_v=
}}
{{Starbox detail
|temperature=44561 ± 675
|gravity=5.23 ± 0.12
}}
{{Starbox catalog
|names=SDSS J093320.86+441705.4}}
{{Starbox reference
|Simbad=US+708}}
{{Starbox end}}
US 708 is a hyper-velocity class O subdwarf in Ursa Major, in the halo of the Milky Way Galaxy. One of the fastest-moving stars in the galaxy, the star was first surveyed in 1982.{{cite web | url=https://www.forbes.com/sites/ericmack/2015/03/08/shrapnel-star-spotted-setting-galactic-speed-record/ | work = Forbes magazine | title = 'Shrapnel' Star Sets Milky Way Speed Record | author = Eric Mack | date = 2015-03-08 | access-date=March 11, 2015}}
Discovery
US 708 was first discovered in 1982 by Peter Usher and colleagues of Pennsylvania State University as a faint blue object in the Milky Way halo. Sloan Digital Sky Survey measured the star again in 2005.
Research
In 2015, Stephan Geier of the European Southern Observatory led a team that reported in Science that the velocity of the star was {{convert|1,200| km/s|km/h mph|abbr=on}}, the highest ever recorded in the galaxy at that time. The star's high velocity was originally suspected to be caused by the massive black 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.
However, closer study suggested it had been one element of a pair of close binary stars.{{cite web | url=http://www.iflscience.com/space/supernova-expels-star-record-speed | title=IflScience | date=7 March 2015 | access-date=March 11, 2015}}
Its companion had already entered its white dwarf stage when US 708 entered its red 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 go supernova, which triggered US 708 being flung away at its high velocity, not by the black hole at the center of our galaxy.{{cite web | url=http://www.techtimes.com/articles/37749/20150306/star-us-708-is-hurtling-out-of-milky-way-and-heres-why.htm | title=TechTimes | date=6 March 2015 | access-date=March 11, 2015}} 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.{{cite web | url=http://www.ifa.hawaii.edu/info/press-releases/fastest_star/ | title = Fastest Star in Our Galaxy Propelled by a Thermonuclear Supernova | access-date=March 11, 2015 | publisher = Institute for Astronomy, University of Hawaii }}{{cite web | url=https://arstechnica.com/science/2015/03/fastest-star-leaving-our-galaxy-was-blasted-out-by-a-supernova/ | title= Fastest star leaving our galaxy was blasted out by a supernova: A double-detonation supernova spits out a hypervelocity hot dwarf | publisher = Arstechnica | access-date=March 11, 2015 | date = March 5, 2015 | author = John Timmer }}
Structure
The star is a high speed rotating, dense helium 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 the Echellette Spectrograph and Imager attached to the 10 meter Keck II telescope in Hawaii.{{cite web | url=http://news.discovery.com/space/astronomy/fastest-star-ever-found-will-escape-from-the-galaxy-150305.htm | title=DNews | access-date=March 11, 2015 | archive-date=May 12, 2015 | archive-url=https://web.archive.org/web/20150512111025/http://news.discovery.com/space/astronomy/fastest-star-ever-found-will-escape-from-the-galaxy-150305.htm | url-status=dead }} Its velocity exceeds the escape velocity of our galaxy.{{cite web | url=http://www.keckobservatory.org/recent/entry/thermonuclear_supernova_ejects_galaxys_fastest_star | title=Thermonuclear Supernova Ejects Galaxy's Fastest Star | publisher=KeK | access-date=March 11, 2015 | archive-date=June 6, 2018 | archive-url=https://web.archive.org/web/20180606125715/http://www.keckobservatory.org/recent/entry/thermonuclear_supernova_ejects_galaxys_fastest_star | url-status=dead }}
See also
- List of star extremes
- S5-HVS1 – fastest moving star as of November 2019
References
{{Reflist|refs=
{{cite journal
| arxiv = 1503.01650| doi=10.1126/science.1259063
| pmid=25745168
| title = The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
| journal=Science
| volume=347
| issue=6226
| pages=1126–8
| publisher = Science magazine
|author1=Stephan Geier |author2=F. Fürst |author3=E. Ziegerer |author4=T. Kupfer |author5=U. Heber |author6=A. Irrgang |author7=B. Wang |author8=Z. Liu |author9=Z. Han |author10=B. Sesar |author11=D. Levitan |author12=R. Kotak |author13=E. Magnier |author14=K. Smith |author15=W. S. Burgett |author16=K. Chambers |author17=H. Flewelling |author18=N. Kaiser |author19=R. Wainscoat |author20=C. Waters | date = 2015-03-06
| quote = Hypervelocity stars (HVSs) travel with velocities so high that they exceed the escape velocity of the Galaxy.
|bibcode = 2015Sci...347.1126G | s2cid=206561078
}}
{{cite news
| url = http://www.sci-news.com/astronomy/science-us708-hypervelocity-star-supernova-galactic-speed-record-02571.html
| title = US 708: Hypervelocity Star Ejected by Supernova Breaks Galactic Speed Record
| publisher = Science News
| date = 2015-03-06
| access-date = 2015-03-10
| quote = 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.
}}
{{cite news
| url = https://www.nytimes.com/2015/03/10/science/fastest-star-in-the-galaxy-got-an-unusual-start.html
| title = Fastest Star in the Galaxy Got an Unusual Start
| work = New York Times
| author = Douglas Quenqua
| date = 2015-03-10
| page = D4
| access-date = 2015-03-10
| quote = 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.
}}
{{cite news
| url = http://www.astronomy.com/news/2015/03/thermonuclear-supernova-ejects-galaxys-fastest-star
| title = Thermonuclear supernova ejects galaxy's fastest star
| publisher = Astronomy magazine
| date = 2015-03-09
| access-date = 2015-03-11
| quote = 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.
}}
}}
{{2015 in space}}{{Ursa Major}}