These
image from NASA's Hubble Space Telescope show SN 2012au, a supernova
explosion that was the subject of a recent study that included
researchers from the CfA. Credit: NASA/STScI. High Resolution (jpg) - Low Resolution (jpg)
Cambridge, MA - The
explosions of stars, known as supernovae, can be so bright they
outshine their host galaxies. They take months or years to fade away,
and sometimes, the gaseous remains of the explosion slam into
hydrogen-rich gas and temporarily get bright again – but could they
remain luminous without any outside interference?
That's what Dan Milisavljevic, an assistant professor of physics and
astronomy at Purdue University, believes he saw six years after "SN
2012au" exploded. Until recently, Milisavlievic was at the
Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass.
"We haven't seen an explosion of this type, at such a late timescale,
remain visible unless it had some kind of interaction with hydrogen gas
left behind by the star prior to explosion," he said. "But there's no
spectral spike of hydrogen in the data – something else was energizing
this thing."
As large stars explode, their interiors collapse down to a point at
which all of their particles become neutrons. If the newly born star has
a magnetic field and rotates fast enough, it can accelerate nearby
charged particles and become what astronomers call a pulsar wind nebula.
This is most likely what happened to SN 2012au, according to findings
published in The Astrophysical Journal Letters. Other co-authors include Dan Patnaude and John Raymond, also from the CfA.
"We know that supernova explosions produce these types of rapidly
rotating neutron stars, but we never saw direct evidence of it at this
unique time frame," Milisavljevic said. "This a key moment when the
pulsar wind nebula is bright enough to act like a lightbulb illuminating
the explosion's outer ejecta."
SN 2012au was already known to be extraordinary – and strange – in
many ways. Although the explosion wasn't bright enough to be termed a
"superluminous" supernova, it was extremely energetic and long-lasting,
and dimmed in a similarly slow light curve.
Milisavljevic predicts that if researchers continue to monitor the
sites of extremely bright supernovae, they might see similar
transformations.
"If there truly is a pulsar or magnetar wind nebula at the center of
the exploded star, it could push from the inside out and even accelerate
the gas," he said. "If we return to some of these events a few years
later and take careful measurements, we might observe the oxygen-rich
gas racing away from the explosion even faster."
Superluminous supernovae are a hot topic in transient astronomy.
They're potential sources of gravitational waves and black holes, and
astronomers think they might be related to other kinds of explosions,
like gamma ray bursts and fast radio bursts. Researchers want to
understand the fundamental physics behind them, but they’re difficult to
observe because they’re relatively rare and happen so far from Earth.
Only the next generation of telescopes including the Giant Magellan
Telescope, which astronomers have dubbed "Extremely Large Telescopes,"
will have the ability to observe these events in such detail.
"This is a fundamental process in the universe. We wouldn't be here
unless this was happening," Milisavljevic said. "Many of the elements
essential to life come from supernova explosions – calcium in our bones,
oxygen we breathe, iron in our blood – I think it's crucial for us, as
citizens of the universe, to understand this process."
Headquartered
in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics
(CfA) is a collaboration between the Smithsonian Astrophysical
Observatory and the Harvard College Observatory. CfA scientists,
organized into six research divisions, study the origin, evolution and
ultimate fate of the universe.
For more information, contact:
Megan Watzke
Harvard-Smithsonian Center for Astrophysics
+1 617-496-7998
mwatzke@cfa.harvard.edu
Peter Edmonds
Harvard-Smithsonian Center for Astrophysics
+1 617-571-7279
pedmonds@cfa.harvard.edu
