Detonating white dwarfs as supernovae

October 4, 2016, American Museum of Natural History
Hubble Space Telescope image of supernova 1994D in galaxy NGC 4526. Credit: NASA/ESA

A new mathematical model created by astrophysicists at the American Museum of Natural History details a way that 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 the Monthly Notices of the Royal Astronomical Society, could improve our understanding of how Type Ia supernovae 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, 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 visualized 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 spiraling 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 LISA, a space-based observatory expected to launch in 2029.

"If we're right, LISA 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."

Explore further: Finding hints of gravitational waves in the stars

More information: B. McKernan et al, On the resonant detonation of sub-Chandrasekhar mass white dwarfs during binary inspiral, Monthly Notices of the Royal Astronomical Society (2016). DOI: 10.1093/mnras/stw2068

Related Stories

Finding hints of gravitational waves in the stars

September 22, 2014

Scientists have shown how gravitational waves—invisible ripples in the fabric of space and time that propagate through the universe—might be "seen" by looking at the stars. The new model proposes that a star that oscillates ...

Image: Hubble Investigates Stellar Shrapnel

August 22, 2016

Several thousand years ago, a star some 160,000 light-years away from us exploded, scattering stellar shrapnel across the sky. The aftermath of this energetic detonation is shown here in this striking image from the NASA/ESA ...

Binary white dwarf stars

May 4, 2011

(PhysOrg.com) -- When a star like our sun gets to be very old, after another seven billion years or so, it will no longer be able to sustain burning its nuclear fuel.

Two dying stars reborn as one (w/ video)

April 6, 2011

White dwarfs are dead stars that pack a Sun's-worth of matter into an Earth-sized ball. Astronomers have just discovered an amazing pair of white dwarfs whirling around each other once every 39 minutes. This is the shortest-period ...

Recommended for you

Researchers make coldest quantum gas of molecules

February 21, 2019

JILA researchers have made a long-lived, record-cold gas of molecules that follow the wave patterns of quantum mechanics instead of the strictly particle nature of ordinary classical physics. The creation of this gas boosts ...

Sculpting stable structures in pure liquids

February 21, 2019

Oscillating flow and light pulses can be used to create reconfigurable architecture in liquid crystals. Materials scientists can carefully engineer concerted microfluidic flows and localized optothermal fields to achieve ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Solon
not rated yet Oct 05, 2016
Alice laughed. "There's no use trying," she said: "one can't believe impossible things."
"I daresay you haven't had much practice," said the Astrophysicist. "When I was your age, I always did it for half-an-hour a day. Why, sometimes I've believed as many as six impossible things before breakfast."

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.