RX J1856.5-3754
Encyclopedia
RX J1856.5-3754
is a nearby neutron star
in Corona Australis
. It is believed to have been created by a supernova
explosion of its companion star about one million years ago and is moving 108 km/s across the sky. It was discovered in 1992, and observations in 1996 appeared to confirm that it was a neutron star
, the closest neutron star to Earth
yet discovered. It was originally thought to be about 150–200 light-year
s away, but further observations using the Chandra X-ray Observatory
in 2002 appear to show that its distance is greater—about 400 light-years. It was once proposed that RX J1856.5-3754 was too small to be a neutron star and may therefore in fact be a quark star
(see also 3C58
). However, this theory is not currently considered to have much supporting evidence.
By combining Chandra X-ray Observatory
and Hubble Space Telescope
data, astronomers previously found that RX J1856 radiates like a solid body with a temperature of 700,000 degrees Celsius and has a diameter of about 4—8 km. This estimated size was too small to reconcile with the standard models of neutron stars, therefore it was suggested that it might be a quark star
. However, later refined analysis of improved Chandra and Hubble observations revealed that the surface temperature of the star is lower, only 434,000 degrees, and respectively the radius is larger, about 14 km (with account of the effects of General Relativity
the observed radius appears about 17 km). Thus, RX J1856.5-3754 is now excluded from the list of quark star candidates.
RX J1856 is one of the Magnificent Seven
, a group of young neutron stars within 500 parsecs of Earth.
is a nearby neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
in Corona Australis
Corona Australis
Corona Australis or Corona Austrina is a constellation. Its name means "southern crown", and it contrasts with Corona Borealis, the northern crown...
. It is believed to have been created by a supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
explosion of its companion star about one million years ago and is moving 108 km/s across the sky. It was discovered in 1992, and observations in 1996 appeared to confirm that it was a neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
, the closest neutron star to Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
yet discovered. It was originally thought to be about 150–200 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away, but further observations using the Chandra X-ray Observatory
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
in 2002 appear to show that its distance is greater—about 400 light-years. It was once proposed that RX J1856.5-3754 was too small to be a neutron star and may therefore in fact be a quark star
Quark star
A quark star or strange star is a hypothetical type of exotic star composed of quark matter, or strange matter. These are ultra-dense phases of degenerate matter theorized to form inside particularly massive neutron stars....
(see also 3C58
3C58
3C58 or 3C 58 is a pulsar and surrounding synchrotron nebula within the Milky Way that is possibly associated with the supernova SN 1181. There are, however, signs that indicate that it could be several thousand years old, and thus not associated with that supernova...
). However, this theory is not currently considered to have much supporting evidence.
By combining Chandra X-ray Observatory
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
and Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
data, astronomers previously found that RX J1856 radiates like a solid body with a temperature of 700,000 degrees Celsius and has a diameter of about 4—8 km. This estimated size was too small to reconcile with the standard models of neutron stars, therefore it was suggested that it might be a quark star
Quark star
A quark star or strange star is a hypothetical type of exotic star composed of quark matter, or strange matter. These are ultra-dense phases of degenerate matter theorized to form inside particularly massive neutron stars....
. However, later refined analysis of improved Chandra and Hubble observations revealed that the surface temperature of the star is lower, only 434,000 degrees, and respectively the radius is larger, about 14 km (with account of the effects of General Relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
the observed radius appears about 17 km). Thus, RX J1856.5-3754 is now excluded from the list of quark star candidates.
RX J1856 is one of the Magnificent Seven
The Magnificent Seven (neutron stars)
The Magnificent Seven is the informal name of a group of isolated young cooling neutron stars near to Earth . These objects are also known under the names XDINS and XTINS .-History:The first to fit this classification was RX J1856.5-3754, which was discovered by Walter et al...
, a group of young neutron stars within 500 parsecs of Earth.
External links
- The Mystery of the Lonely Neutron Star, European Southern ObservatoryEuropean Southern ObservatoryThe European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
press release, September 11, 2000. Accessed online at spaceref.com May 20, 2007. - Closest Known Neutron Star Races Across Sky (space.com)
- Is RX J185635-375 a Quark Star?
- APOD: 2002 April 14 - RX J185635-375: Candidate Quark Star
- Bare Quark Stars or Naked Neutron Stars? The Case of RX J1856.5-3754
- RX J185635-3754 - an Isolated Neutron Star
- News Release STScI-1997-32: Hubble Sees a Neutron Star Alone in Space