Huge explosions on Earth may be one-time deals, but their resounding echoes can give us another bang for our buck if conditions are right.
Strangely,
the same is true in the depths of space.
Astronomers
recently captured a supernova's blinding flash "echoing" off dust 400
light-years from the detonation site in the Large Magellanic Cloud — which
means Earthly observers may have seen the original blast 400 years ago. Because
a star's death rattle produced the light, scientists can use the new
observations to effectively peer into the past.
"We
have a chance here to see the supernova in both the past and the present,"
said Armin Rest, an astronomer at Harvard University who co-authored one of two
new studies on supernovae. "We can see light from the blast bouncing off
of dust, and we can also see the supernova remnants. It's kind of like having a
time machine."
Rest and
other astronomers used NASA's Chandra
X-ray observatory, Europe's XMM-Newton observatory and the Gemini observatory
to gather their findings, detailed in two studies in a recent issue of The Astrophysical
Journal.
Blast
from the past
Supernova
remnant (SNR) 0509-67.5, as the dead star's remains are known, lies about
160,000 light-years from Earth — which means the light we see from actually began
its journey 160,000 years ago. The newly observed echo was created in this
manner: Light from the blast traveled for 400 years across the sky, not heading
our way, then bounced off stuff and began its journey toward us.
That means light
from the original blast, which headed directly this way, would have reached
Earth 400 years ago. That explosion is no longer observable, but now the echo
has been seen.
Rest said
supernova remnants like SNR 0509-67.5 stick around a long time for astronomers
to analyze, but noted it's nearly impossible to see them clearly outside of our
galaxy. It's also difficult to figure out exactly what kinds of stellar
explosions create remnants.
"Unless
you record light directly from a supernova when it happens, you get second-hand
information like at a crime scene," Rest said. "Just like it's hard
to identify the killer, it's difficult to determine the type of supernova
explosion."
It's
easiest to catch a supernova under way, he said, but they typically last only a
few days.
"We've
recorded only a few supernovae in the past couple of thousand years," Rest
said, noting that telescopes can now efficiently detect new supernovae across
the universe, but ancient explosions are trickier to analyze.
Ancient
light
But that's
where light echoes from violent stellar deaths come in handy, Rest said. The
teams of astronomers monitored the echoing light waves of SNR 0509-67.5 for
about five years to create a time-lapse video of the action.
"As
the light spreads out from the blast, interstellar gas and dust reflect it
around the universe," he said, comparing it to light reflecting brightly
in fog. "In this case, it took a longer path to get to Earth than the
direct light."
In spite of
its older age, he explained, that reflected light is as good as seeing it
directly from a supernova.
"Everything
about the light is preserved, so we can analyze the spectrum and pinpoint the
supernova type, including what kinds of elements it produced," Rest said,
noting that carbon, oxygen and heavier atoms necessary for life can be detected
in the light spectra, or signature.
Light
echoes from SNR 0509-67.5 aren't
the first ever to be seen, but Rest said their importance is growing in the
field.
"Our
ability to see light echoes is improving every year now," Rest said,
noting advancements in detectors and other telescope technology. "We can
compare these [light echoes] to their supernova remnants and also better
estimate how far away they are. Distance is one of the hardest things to
determine in astronomy."
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