Artist’s impression of a Supernova
Credit: NASA/ESA/G. Bacon (STSci)
iPTF14hls grew bright and dim again at least five times over two years. This behavior has never been seen in previous supernovae, which typically remain bright for approximately 100 days and then fade. Adapted from Arcavi et al. 2017, Nature. Credit: LCO/S. Wilkinson
An image taken by the Palomar Observatory Sky Survey reveals a
possible explosion in the year 1954 at the location of
iPTF14hls (left), not seen in a later image taken in 1993
(right). Supernovae are known to explode only once, shine for a
few months and then fade, but iPTF14hls experienced at least
two explosions, 60 years apart. Adapted from Arcavi et al. 2017,
Nature.
Lead author Iair Arcavi, a NASA Einstein postdoctoral fellow at LCO and the University of California Santa Barbara, visiting the Keck Observatory twin 10-meter optical/infrared telescopes on Maunakea, Hawaii. Credit: I. Arcavi
Maunakea,
Hawaii – An international team of
astronomers led by Las Cumbres Observatory (LCO) has made a bizarre discovery; a
star that refuses to stop shining.
Supernovae,
the explosions of stars, have been observed in the
thousands and in all cases
they marked the death of a star.
But
in a study published today in the journal Nature, the team discovered a remarkable exception; a star that
exploded multiple times over a period of more than fifty years.
Their observations, which include data from W. M. Keck Observatory on Maunakea, Hawaii, are
challenging existing theories on these cosmic catastrophes.
“The
spectra we obtained at Keck Observatory showed that this supernova looked like
nothing we had ever seen before. This, after discovering nearly 5,000
supernovae in the last two decades,” said Peter Nugent, Senior Scientist and
Division Deputy for Science Engagement in the Computational Research Division
at Lawrence Berkeley National Laboratory who co-authored the study. “While the
spectra bear a resemblance to normal hydrogen-rich core-collapse supernova
explosions, they grew brighter and dimmer at least five times more slowly,
stretching an event which normally lasts 100 days to over two years.”
Researchers
used the Low Resolution Imaging Spectrometer (LRIS) on the Keck I telescope to
obtain spectrum of the star’s host galaxy, and the Deep Imaging and
Multi-Object Spectrograph (DEIMOS) on Keck II to obtain high-resolution spectra
of the unusual star itself.
The supernova, named
iPTF14hls, was discovered in September of 2014 by the Palomar
Transient Factory. At the time, it looked like an ordinary
supernova. Several months later, LCO astronomers noticed the
supernova was growing brighter again after it had faded.
When astronomers went
back and looked at archival data, they were astonished to
find evidence of an explosion in 1954 at the same
location. This star somehow survived that explosion and exploded
again in 2014.
“This supernova breaks
everything we thought we knew about how they work. It’s
the biggest puzzle I’ve encountered in almost a decade of studying
stellar explosions,” said lead author Iair Arcavi, a NASA Einstein
postdoctoral fellow at LCO and the University of California Santa
Barbara.
The study calculated
that the star that exploded was at least 50 times more massive
than the sun and probably much larger. Supernova iPTF14hls
may have been the most massive stellar explosion ever seen.
The size of this explosion could be the reason that our
conventional understanding of the death of stars failed to explain
this event.
Supernova iPTF14hls may be
the first example of a “Pulsational Pair Instability Supernova.”
“According to this theory,
it is possible that this was the result of star so massive and hot that it
generated antimatter in its core,” said co-author Daniel Kasen, an associate
professor in the Physics and Astronomy Departments at UC Berkeley and a
scientist at Lawrence Berkeley Lab. “That would cause the star to go violently
unstable, and undergo repeated bright eruptions over periods of years.”
That process may even repeat over decades before the star’s large final explosion and collapse to a black hole.
“These explosions were
only expected to be seen in the early universe and should
be extinct today. This is like finding a dinosaur still alive
today. If you found one, you would
question whether it truly was a dinosaur,” said Andy Howell,
leader of the LCO supernova group and co-author of the study.
Indeed, the “Pulsational
Pair Instability” theory may not fully explain all the data
obtained for this event. For example, the energy released by
the supernova is more than the theory predicts. This supernova may be
something completely new.
Astronomers continue
to monitor iPTF14hls, which remains bright three years after
it was discovered.
“This is one of those head-scratcher type of events,” said Nugent.
“At first we thought it was completely normal and boring. Then it just kept
staying bright, and not changing, for month after month. Piecing it all
together, from our observations at Palomar Transient Factory, Keck Observatory,
LCOGT, and even the images from 1954 in the Palomar Sky Survey, has started to
shed light on what this could be. I would really like to find another one like
this.”
Media Contact:
Mari-Ela Chock, Communications Officer
mchock@keck.hawaii.edu
(808) 554-0567
Source: W.M. Keck Observatory
About W.M. Keck Observatory
The W. M. Keck Observatory telescopes are
among the most scientifically productive on Earth. The two, 10-meter
optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii
feature a suite of advanced instruments including imagers, multi-object
spectrographs, high-resolution spectrographs, integral-field spectrometers, and
world-leading laser guide star adaptive optics systems.
Some of the data presented herein were obtained at
Keck Observatory, which is a private 501(c) 3 non-profit organization operated
as a scientific partnership among the California Institute of Technology, the
University of California, and the National Aeronautics and Space
Administration. The Observatory was made possible by the generous financial
support of the W. M. Keck Foundation.
The authors wish to
recognize and acknowledge the very significant cultural role and reverence that
the summit of Maunakea has always had within the indigenous Hawaiian
community. We are most fortunate to have the opportunity to conduct
observations from this mountain.
