One of the more recent finding of astronomy is that stars,
as far apart as they are, really like to form pairs. These so-called
“binary star systems” are everywhere, and as new evidence comes in we’re
beginning to see that binary systems may be just as common as the
“regular” kind; for instance, about half the exoplanets found thus far orbit in binary systems. This fact may end up being very helpful to astronomers indeed, since new evidence
from Harvard and over a dozen other universities show that Type Ia
supernovae may be born of binary stars. This could help settle a
long-standing debate over the origin of this specific type of supernova,
and confirm its usefulness to science.
A Type Ia supernova is sometimes called a “standard candle,”
though not so much anymore, because the intensity of type of signal
released is believed to be standardized. If that’s true, then they could
be hugely helpful to mapping the universe, estimating distances with
far better accuracy than other methods — but only if it’s true. To
figure that out, we’d need to actually understand what’s causing these
supernovae, and there was never any concrete proof to settle the
argument — now, one preexisting theory has some serious new support.
A
supernova occurs when a star above a certain mass threshold cools down
below a certain temperature threshold — essentially, the expansive force
reduces far enough that the inward force of gravity causes a core
collapse, implosion, and supernova. Stars lighter than the threshold
mass (called the Chandrasekhar Limit) won’t go supernova, while those
over the limit will, and the star’s exact amount of mass beyond that
threshold does a lot to dictate the intensity of the resulting
destruction.
To explain the oddly reliable characteristics of Type Ia
supernovae, astronomers imagined a binary star system in which one
cooled star (white dwarf) orbits close enough to a red giant the white
dwarf can suck up matter and grow. If this heavy white dwarf were very
near to the Chandrasekhar Limit, the input of new mass could push the
core over the limit after the star has already cooled down. This would cause the star to go supernova the instant
it cross the mass threshold, meaning that its intensity should be
fairly reliable, resulting from precisely the same process and final
mass. But inconsistencies in standard candle readings, and the
continuing inability to really prove where exactly they come from, meant
that Type Ia supernovae data was shunned by many physicists.
This new paper
presents a burst of light as evidence of a companion star in an
observed supernova — blue light, particularly. This occurs when a nearby
supernova heats up one side of a star, causing that side to become
bluer (remember that in astronomy, blue stars are hotter than red ones).
Their data show that the event could have been caused by the
binary-companion model, but it’s not proven quite yet. The researchers
point out that this observation needs to be replicated many more times
to prove that Type Ia supernovae occur only in binary systems, which is the theory.
As far as its usefulness to science, it doesn’t really
matter what the final model for Type Ia supernovae ends up being, just
so long as it’s reliable. If it does turn out that our standard candles
come from binary systems, the sheer frequency of the signals is
interesting — there must be a lot of
white-dwarf-red-giant-close-binary-systems.
Now that the first observation is nailed down, we’ll need to
wait for the rest of the observations to come in. Let’s hope the
evidence does confirm that astronomers really do have a standard candle
in their toolbox.
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