Artist’s impression of two white dwarf stars destined to merge and create a Type Ia supernova
Image of the planetary nebula Henize 2-428 from the Very Large Telescope
The planetary nebula Henize 2-428 in the constellation of Aquila
Wide-field view of the sky around the planetary nebula Henize 2-428
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Video
Artist’s impression of two white dwarf stars merging and creating a Type Ia supernova
First pair of merging stars destined to become supernova found
Astronomers using ESO facilities in
combination with telescopes in the Canary Islands have identified two
surprisingly massive stars at the heart of the planetary nebula Henize
2-428. As they orbit each other the two stars are expected to slowly get
closer and closer, and when they merge, about 700 million years from
now, they will contain enough material to ignite a vast supernova
explosion. The results will appear online in the journal Nature on 9
February 2015.
The team of astronomers, led by Miguel Santander-García (Observatorio Astronómico Nacional, Alcalá de Henares, Spain; Instituto de Ciencia de Materiales de Madrid (CSIC), Madrid, Spain), has discovered a close pair of white dwarf stars
— tiny, extremely dense stellar remnants — that have a total mass of
about 1.8 times that of the Sun. This is the most massive such pair yet
found [1] and when these two stars merge in the future they will create a runaway thermonuclear explosion leading to a Type Ia supernova [2].
The team who found this massive pair actually set out to
try to solve a different problem. They wanted to find out how some stars
produce such strangely shaped and asymmetric nebulae late in their
lives. One of the objects they studied was the unusual planetary nebula [3] known as Henize 2-428.
“When we looked at this object’s central star with
ESO’s Very Large Telescope, we found not just one but a pair of stars at
the heart of this strangely lopsided glowing cloud,” says coauthor Henri Boffin from ESO.
This supports the theory that double central stars may
explain the odd shapes of some of these nebulae, but an even more
interesting result was to come.
"Further observations made with telescopes in the
Canary Islands allowed us to determine the orbit of the two stars and
deduce both the masses of the two stars and their separation. This was
when the biggest surprise was revealed," reports Romano Corradi, another of the study's authors and researcher at the Instituto de Astrofísica de Canarias (Tenerife, IAC).
They found that each of the stars has a mass slightly less
than that of the Sun and that they orbit each other every four hours.
They are sufficiently close to one another that, according to the
Einstein’s theory of general relativity, they will grow closer and
closer, spiralling in due to the emission of gravitational waves, before
eventually merging into a single star within the next 700 million
years.
The resulting star will be so massive that nothing can then
prevent it from collapsing in on itself and subsequently exploding as a
supernova. "Until now, the formation of supernovae Type Ia by the merging of two white dwarfs was purely theoretical," explains David Jones, coauthor of the article and ESO Fellow at the time the data were obtained. “The pair of stars in Henize 2-428 is the real thing!”
"It's an extremely enigmatic system," concludes Santander-García. "It
will have important repercussions for the study of supernovae Type Ia,
which are widely used to measure astronomical distances and were key to
the discovery that the expansion of the Universe is accelerating due to
dark energy".
Notes
[1] The Chandrasekhar limit
is the greatest mass that a white dwarf star can have and support
itself against gravitational collapse. It has a value of about 1.4 times
the mass of the Sun.
[2] Type Ia supernovae occur when a
white dwarf star acquires extra mass — either by accretion from a
stellar companion or by merging with another white dwarf. Once the mass
exceeds the Chandrasekhar limit the star loses its ability to support
itself and starts to contract. This increases the temperature and a
runaway nuclear reaction occurs and blows the star to pieces.
[3] Planetary nebulae have nothing to
do with planets. The name arose in the eighteenth century as some of
these objects resembled the discs of the distant planets when seen
through small telescopes.
More Information
This research was presented in a paper
entitled “The double-degenerate, super-Chandrasekhar nucleus of the
planetary nebula Henize 2-428” by M. Santander-García et al., to appear
online in the journal Nature on 9 February 2015.
The team is composed of M. Santander-García (Observatorio Astronómico
Nacional, Alcalá de Henares, Spain; Instituto de Ciencia de Materiales
de Madrid (CSIC), Madrid, Spain), P. Rodríguez-Gil (Instituto de
Astrofísica de Canarias, La Laguna, Tenerife, Spain [IAC]; Universidad
de La Laguna, Tenerife, Spain), R. L. M. Corradi (IAC; Universidad de La
Laguna), D. Jones (IAC; Universidad de La Laguna), B. Miszalski (South
African Astronomical Observatory, Observatory, South Africa [SAAO]), H.
M. J. Boffin (ESO, Santiago, Chile), M. M. Rubio-Díez (Centro de
Astrobiología, CSIC-INTA, Torrejón de Ardoz, Spain) and M. M. Kotze
(SAAO).
ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive ground-based astronomical
observatory by far. It is supported by 16 countries: Austria, Belgium,
Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy,
the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the
United Kingdom, along with the host state of Chile. ESO carries out an
ambitious programme focused on the design, construction and operation of
powerful ground-based observing facilities enabling astronomers to make
important scientific discoveries. ESO also plays a leading role in
promoting and organising cooperation in astronomical research. ESO
operates three unique world-class observing sites in Chile: La Silla,
Paranal and Chajnantor. At Paranal, ESO operates the Very Large
Telescope, the world’s most advanced visible-light astronomical
observatory and two survey telescopes. VISTA works in the infrared and
is the world’s largest survey telescope and the VLT Survey Telescope is
the largest telescope designed to exclusively survey the skies in
visible light. ESO is a major partner in ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre European Extremely Large Telescope, the E-ELT,
which will become “the world’s biggest eye on the sky”.
Link
Contacts
Miguel Santander-García
Observatorio Astronómico Nacional
Alcalá de Henares, Spain
Tel: +34 670243627
Email: m.santander@oan.es
Henri Boffin
ESO
Santiago, Chile
Tel: +49 89 3200 3126
Email: hboffin@eso.org
Richard Hook
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
