Astronomers Spot a Supernova in the Making

By Sarah Scoles | February 9, 2015 2:14 pm
Artist’s impression of two white dwarf stars destined to merge and create a Type Ia supernova. Credit: ESO/L. Calçada

Artist’s impression of two white dwarf stars destined to merge and create a Type Ia supernova. Credit: ESO/L. Calçada

Astronomers can see into the future of the two superdense stars racing around the center of planetary nebula Henize 2-428. And it doesn’t look good.

Their racetrack is slowly (but steadily) shrinking. And in 700 million years, they will crash into each other, igniting a Type Ia supernova. In over a century of astronomers studying supernovae, this is the first time they’ve seen this type of supernova in the making.

Life of a White Dwarf

Type Ia supernovae are the game-over of some normal-sized stars, which spend most of their days fusing hydrogen into helium. As they age, they begin turning that lifetime’s supply of helium into carbon and oxygen. But they don’t have enough energy to concoct something new, and so their carbon and oxygen build up into a hot, dense core.

In a death-rattle, the stars blow off their outer hydrogen and helium layers. The exhaled gas forms pretty planetary nebulae. But the stars themselves — now called white dwarfs — just cool off, growing dimmer like a recently switched-off electric oven coil.

Sometimes, though, they get a jolt — some extra mass that ignites a reaction that ends in a supernova. Astronomers have spent years trying to figure out where that mass comes from. For a long time, it seemed exploding dwarfs just stole material from giant companion stars. But more recently, they’ve begun to suspect that two white dwarfs can also get the job done — if they work together.

Image of the planetary nebula Henize 2-428 from the Very Large Telescope. Credit: ESO

Image of the planetary nebula Henize 2-428 from the Very Large Telescope. Credit: ESO

Collision Course

This new result shows that two dwarfs can produce a supernova — or, at least, it will, in 700 million years.

The outcome is, however, pretty certain. Right now the stars orbit around each other every 4.2 hours. Objects that massive, dense, close, and fast disturb the spacetime around them, rippling it like two sharks circling each other. They produce gravitational waves, each of which carries away a little bit of energy, causing the dwarfs to drift closer and closer together.

Once they’re so close that they crash, they become an “it,” with a total mass will be so large (1.8 times the sun’s) it will collapse in on itself and then explode. The stars in Henize 2-428 will become “a star” briefly in 700 million years, before becoming a blast.

Distant Detonation

When white dwarfs go supernova — a subset of explosions called Type Ia — they explode with predictable brightness. That has made them useful as so-called standard candles, to help gauge distances in the far-off universe.

Because of white dwarfs’ misfortunes, we know how far away other galaxies are, and we know how fast they’re moving away from us. We can then calculate how quickly the universe is expanding, and then how powerful dark energy is.

The more we know about how supernovae like the one in Henize 2-428’s, the more standard the candles become. With a known-to-the-Watt brightness, we could tell exactly how far away other galaxies are, and how fast the universe we all live in flies outward.


CATEGORIZED UNDER: Space & Physics, top posts
  • wayne smallwood

    The r-process will create the elements that make up rocky planets, and provide the chemical bases for Life As We Know It (and Life As We don’t Know It, too). Both stars, being White Dwarfs, are rich in 12Carbon, so, among everything else (up through the transuranic elements), there should also be some good carbonados.

    • Ventura Rodriguez Vallejo

      Uncle Al: thanks you for your fascinating comment.
      What doesn’t become evident in it for me (given you use it as term of comparison) is the “Earth’s total power production”. I don’t know the timelapse you’re referring to. A day? A year? Will you please clarify this point? Thanks again and best regards.

      • jcbwell

        Power is an “instantaneous” measure. Integrated over time it’s Energy we discuss. 1000 watts generated for an hour is a kilowatt-hr. But that’s energy, not power. He was discussing the total generating capacity worldwide.

        • Ventura Rodriguez Vallejo

          By answering Dan Backer’s question, Uncle Al has answered mine, too. It is man produced and consumed energy in 24 hours (one day) worldwide. These are satisfactory data missing in Uncle Al’s first comment, and gives the proper comparison scale term I was looking for. If you say, for exmple, that during World War II, Hiroshima was bombed with 20 kTons of explosive energy, you must add if this amount was spread in a lapse of 10*10^-4 seconds or 10*10^40 seconds, what was been a very different matter, don’t you agree?

  • Uncle Al

    They produce gravitational waves, each of which carries away a little bit of energy” A “little” bit? Earth’s total energy production is about 1.4×10^13 watts. Gravitational radiation radiated power is

    P = -(32/5)(G^4/c^5)[(m1 + m2)(m1m2)^2]/r^5

    Where G = Newton’s constant, c = lightspeed, m1 and m2 are the bodies’ masses, r is their radial separation. Your “little bit” is currently in the neighborhood of, oh, maybe 10^20 watts. Orbital decay is proportional to the inverse third power of their radial separation. Not much happens for a long time, then WHAMMO! When they merge, orbital angular momentum must be conserved as the much smaller radius composite body’s rotation. In the last few milliseconds before merger, orbital velocity will be strongly relativistic Simple irrotational models are nowhere near what will transpire.

    • dan becker

      Uncle Al,
      For those of us not up on astronomical mathematics, what is the Earth’s energy production? You mean heat, or rotational, or…?

      • Uncle Al

        Burned fuels, nuclear, solar, wind… man-made and net delivered to do something, averaged 24-hr output worldwide.

    • Phil

      Okay, so, based on what it is you just said, “…Henize 2-428 will become “a star” briefly in 700 million years…”, how long is ‘briefly’?

    • Come on think!

      perhaps that little bit was a proportional little.

      • Guest

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  • Gary Ronan

    Looks like A Shmoo!

  • Bob Rehmer

    I’ll check back in 700 million (+/-) years.


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