Hubble Space Telescope image of the type Ia supernova 1994D (lower left) in galaxy NGC 4526.
Credit: NASA/ESA, the Hubble Key Project Team and the High-Z Supernova Search Team.
Credit: NASA/ESA, the Hubble Key Project Team and the High-Z Supernova Search Team.
A new mathematical model created by astrophysicists at the American Museum of Natural History,
New York, describes how dead stars called white dwarfs could detonate,
producing a type of explosion that is instrumental to measuring the
extreme distances in our universe. The mechanism, described in a paper
in Monthly Notices of the Royal Astronomical Society, could improve our understanding of how t form.
"Type Ia supernovae are extremely important objects in physics, best
known for their role in revealing that the expansion of the universe is
accelerating," said paper co-author Saavik Ford, who is a research associate in the Museum’s Department of Astrophysics as well as a professor at the Borough of Manhattan Community College, City University of New York (CUNY); a faculty member at CUNY’s Graduate Center; and a Kavli Scholar at the Kavli Institute for Theoretical Physics. "The problem is that people do not agree on exactly how type Ia supernovae come to be."
Current research indicates that type Ia supernova explosions
originate from binary star systems—two stars orbiting one another—in
which at least one star is a white dwarf,
the dense remains of a star that was a few times more massive than our
Sun. For this study, the scientists investigated how two white dwarfs
might form a supernova.
"The simplest way to create a type Ia supernova is to run two white
dwarfs into one another," Ford said. "In our local universe, there are
very few white dwarf binaries that are close enough to collide. Yet we
see lots of supernovae lighting up our universe, so we know that
something else is probably going on to cause those explosions."
Ford and co-author Barry McKernan, who is also a research associate
in the Museum’s Department of Astrophysics, a professor at the Borough
of Manhattan Community College, CUNY, a faculty member at CUNY’s
Graduate Center, and a Kavli Scholar at the Kavli Institute for
Theoretical Physics, propose the following: White dwarfs are roughly
Earth-sized balls of dense, compressed, degenerate matter that wobble,
or oscillate. When two white dwarfs orbit each other they tug on one
another, emitting gravitational radiation that takes away energy from
their orbit. This causes them to get closer and closer together. During
this process, known as inspiraling, the binary orbit of the stars gets
smaller, the frequency of the tugging gets stronger and, at certain
"sweet spots," it matches an oscillation frequency in at least one of
the white dwarfs. When this happens, a phenomenon called resonance is
produced, which can be visualised by a child being pushed in a
playground swing.
"Pushing your kid in time with the natural interval, or frequency, of
the swing ramps up the energy and gets them higher and higher,"
McKernan said. "There’s a similar effect in our model, where a lock on
the frequency produces a series of rapid jumps in energy that are
deposited into the white dwarfs."
As a result, if enough energy is deposited in the resonating white
dwarf, it could explode before it touches the other one. If the white
dwarf does not explode, the resonance causes the orbit to shrink faster
than predicted by gravitational wave emission alone, so the stars will
crash into each other faster than would normally be expected.
"Basically, we’ve proposed that if you have two white dwarfs spiralling towards each other and you shake one of them the right way for long enough, one will either blow up or you’ll bring the objects closer together faster for an eventual detonation," McKernan said.
Ford and McKernan plan to test their model by combing through data produced by up-and-coming gravitational wave detectors like eLISA, a space-based observatory expected to launch in 2029.
"If we’re right, eLISA may be able to see glitches in the
gravitational waveforms coming from some of the nearest white dwarf
binaries," McKernan said. "That would be amazing to see."
Media Contact
Kendra Snyder, Department of Communications
American Museum of Natural History, New York, USA
Tel: +1 212 496 3419
ksnyder@amnh.org
www.amnh.org
Image and caption
https://www.ras.org.uk/images/stories/press/Supernovae/Supernova%201994D_NASAESA.jpg
Hubble Space Telescope image of the type Ia supernova 1994D (lower left) in galaxy NGC 4526. Credit: NASA/ESA, the Hubble Key Project Team and the High-Z Supernova Search Team
Further Information
Funding for this study was provided by the National Science Foundation grant #s PAARE AST-1153335 and PHY11-25915.
The new work appears in "On the resonant detonation of sub-Chandrasekhar mass white dwarfs during binary inspiral",
B. McKernan and K. E. S. Ford, vol. 463 (2), pp. 2039-2045, Monthly
Notices of the Royal Astronomical Society, Oxford University Press.
Notes for editors
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The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
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