When a massive star runs out fuel, it collapses and explodes as a supernova. Although these explosions are extremely powerful, it is possible for a companion star to endure the blast. A team of astronomers using NASA's Chandra X-ray Observatory and other telescopes has found evidence for one of these survivors.
This hardy star is in a stellar explosion's debris field - also
called its supernova remnant - located in an HII region called DEM L241.
An HII (pronounced "H-two") region is created when the radiation from
hot, young stars strips away the electrons from neutral hydrogen atoms
(HI) to form clouds of ionized hydrogen (HII). This HII region is
located in the Large Magellanic Cloud, a small companion galaxy to the Milky Way.
A new composite image of DEM L241 contains Chandra data (purple) that
outlines the supernova remnant. The remnant remains hot and therefore X-ray
bright for thousands of years after the original explosion occurred.
Also included in this image are optical data from the Magellanic Cloud
Emission Line Survey (MCELS) taken from ground-based telescopes in Chile
(yellow and cyan), which trace the HII emission produced by DEM L241.
Additional optical data from the Digitized Sky Survey (white) are also
included, showing stars in the field.
R. Davies, K. Elliott, and J. Meaburn, whose last initials were
combined to give the object the first half of its name, first mapped DEM
L241 in 1976. The recent data from Chandra revealed the presence of a
point-like X-ray source at the same location as a young massive star
within DEM L241's supernova remnant. (Mouse over the image to see the
location of the survivor companion star.)
Astronomers can look at the details of the Chandra data to glean
important clues about the nature of X-ray sources. For example, how
bright the X-rays are, how they change over time, and how they are
distributed across the range of energy that Chandra observes.
In this case, the data suggest that the point-like source is one component of a binary star system. In such a celestial pair, either a neutron star or black hole
(formed when the star went supernova) is in orbit with a star much
larger than our Sun. As they orbit one another, the dense neutron star
or black hole pulls material away its companion star through the wind of
particles that flows away from its surface. If this result is
confirmed, DEM L241 would be only the third binary containing both a
massive star and a neutron star or black hole ever found in the
aftermath of a supernova.
Chandra's X-ray data also show that the inside of the supernova remnant is enriched in oxygen, neon and magnesium.
This enrichment and the presence of the massive star imply that the
star that exploded had a mass greater than 25 times, to perhaps up to 40
times, that of the Sun.
Optical observations with the South African Astronomical
Observatory's 1.9-meter telescope show the velocity of the massive star
is changing and that it orbits around the neutron star or black hole
with a period of tens of days. A detailed measurement of the velocity
variation of the massive companion star should provide a definitive test
of whether or not the binary contains a black hole.
Indirect evidence already exists that other supernova remnants were
formed by the collapse of a star to form a black hole. However, if the
collapsed star in DEM L241 turns out to be a black hole, it would
provide the strongest evidence yet for such a catastrophic event.
What does the future hold for this system? If the latest thinking is
correct, the surviving massive star will be destroyed in a supernova
explosion some millions of years from now. When it does, it may form a
binary system containing two neutron stars or a neutron star and a black
hole, or even a system with two black holes.
A paper describing these results is available online
and was published in the November 10, 2012 issue of The Astrophysical
Journal. The authors are Fred Seward of the Harvard-Smithsonian Center
for Astrophysics in Cambridge, MA; P. Charles from University of
Southampton, UK; D. Foster from the South African Astronomical
Observatory in Cape Town, South Africa; J. Dickel and P. Romero from
University of New Mexico in Albuquerque, NM; Z. Edwards, M. Perry and R.
Williams from Columbus State University in Columbus, GA.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory in Cambridge, Mass., controls
Chandra's science and flight operations. Source: NASA’s Chandra X-ray Observatory
Fast Facts for DEM L241:
Credit: X-ray: NASA/CXC/SAO/F.Seward et al; Optical: NOAO/CTIO/MCELS, DSS
Scale: Image is 24 arcmin across (1100 light years)
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 05h 36m 00.00s | Dec -67º 35' 09.00"
Constellation: Dorado
Observation Date: 2 pointings on Feb 7 and Feb 8, 2011
Observation Time: 12 hours 47 min
Obs. ID: 12675, 13226
Instrument: ACIS
References: Seward, F. et al, 2012, ApJ, 759, 123; arXiv:1208.1453
Color Code: X-ray (Magenta); Optical (Red, Green, Blue)
Distance Estimate: About 160,000 light years
