On Nov. 11,
1572, astronomer Tycho Brahe observed a bright "new star" — now known
as a supernova — in the constellation Cassiopeia.
Brahe observed
the star, which outshone even Venus in the night sky until it faded from
sight in March 1574.
Now, more
than 400 years later, astronomers have use the Subaru Telescope in Hawaii to
observe "light echoes" from the stellar blast to determine its origin
and type and relate that information to what they see in the supernova remnant
today.
A supernova
occurs when a star dies violently, sending out an extremely bright outburst
of energy.
Some of the
light from the original supernova event bounces off dust particles in
surrounding interstellar clouds and reaches Earth many years after the direct
light passes by; in this case, 436 years ago. These reflections are called
"light echoes."
In
September, scientists used the Faint Object Camera and Spectrograph (FOCAS)
instrument at Subaru, to break apart the light echoes of Supernova 1572 into
the signatures of atoms (spectra) present when the star exploded, bearing all
the information about the nature of the original blast.
"Using
light echoes in supernova remnants is time-traveling in a way, in that it
allows us to go back hundreds of years to observe the first light from a
supernova event," said Tomonori Usuda, lead project astronomer at Subaru.
"We got to relive a significant historical moment and see it as famed
astronomer Tycho Brahe did hundreds of years ago. More importantly, we get to
see how a supernova in our own galaxy behaves from its origin."
This same
team used similar methods to uncover the origin of supernova remnant Cassiopeia
A in 2007.
The results
of the Subaru study, detailed in the Dec. 3 issue of the journal Nature,
showed clear absorption of once-ionized silicon and absence of the hydrogen
H-alpha emission in the light echoes — signatures typical of a Type Ia supernova observed at
maximum brightness of its outburst.
Type Ia supernovae are generally thought to originate from
white dwarf stars in a close binary system. As the gas of the companion star
accumulates onto the white dwarf, the white dwarf is progressively compressed,
and eventually sets off a runaway nuclear reaction inside that eventually leads
to a cataclysmic supernova outburst.
These
supernovae are also the primary source of heavy elements in the universe, and
play an important role as cosmological distance indicators
The Subaru
study found that Tycho's supernova belongs to the majority class of Normal Type
Ia, and, as such, is now the first confirmed and precisely classified supernova
in our galaxy.
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