1. NEWSFOCUS
Burning bright.
The supernova SN 2011fe
(above), first detected in
August 2011, has become
one of the most closely
studied supernovae in
history.
Death of a Star
The discovery of a nearby supernova has brought astrophysicists
Downloaded from www.sciencemag.org on January 4, 2013
closer to understanding a class of stellar explosions. Along with that
success came an unexpected tragedy.
PETER NUGENT DROVE TO WORK ON THE night, having logged in at Berkeley. And as begun taking images and spectra of the super-
morning of 24 August 2011, still oblivious to they often did, the two began chatting over nova, and around 2:30 p.m. California time,
the faraway cosmic explosion that would con- Gmail while going through the results. At Nugent and Sullivan were looking at the first
sume him for weeks ahead. Walking toward 12:40 p.m., Bloom messaged Nugent that he spectroscopic results, puzzling over the kind
the entrance of the National Energy Research had found an object that looked like a super- of supernova it was. After a few minutes of
Scientific Computing Center (NERSC) in nova that had gone off 400 million light-years studying its spectral features, Nugent excit-
Oakland, California, he stopped to watch away. “That’s great,” Nugent responded. edly messaged Sullivan that the object was a
news vans covering protests against a shut- Then, seconds later, Nugent spotted another type Ia—a class of supernova that shines with
down of cell phone service on the Bay Area candidate that looked like a supernova in the such predictable luminosity that astrophysi-
Rapid Transit system. Then Nugent, a theoret- Pinwheel galaxy, only 21 million light-years cists use it as a standard candle for measuring
ical astrophysicist who could be mistaken for away. Because this one was so much closer cosmic distances. Following convention, the
CREDIT: COURTESY OF B. J. FULTON, THE BYRNE OBSERVATORY AT SEDGWICK RESERVE AND THE PALOMAR TRANSIENT FACTORY
a football player if he came thundering down to Earth, it was potentially of greater value researchers named the object SN 2011fe.
a hall, turned his attention away from earthly to astronomers. “I see your $20 and raise Because of their usefulness to cosmol-
matters and dived back into the otherworldly you $100,” Nugent joked. “Dang,” Bloom ogy, type Ias are valuable finds. The one
pursuit of astrophysics. replied, checking it out. that Nugent and his colleagues had discov-
That morning, he had an urgent task: fixing Detecting a newly exploding star or ered was even more valuable because it had
a glitch in a digital pipeline that feeds astro- gamma ray burst tends to quicken the pulse been detected just 11 hours after the super-
nomical images from a 1.2-meter-diameter of astronomers. Because of the transient nova went off, making it the youngest type Ia
survey telescope on Mount Palo- nature of stellar explosions— discovered to date and allowing astrono-
mar to the computers at NERSC.
The pipeline had crashed the Online they can fade away within hours
to days—the moment of discov-
mers to study the explosion from an earlier
stage in its progression than any type Ia seen
night before, leaving thousands sciencemag.org ery marks the beginning of a race before. Nugent sent out an Astronomer’s
Podcast interview
of pictures waiting to be uploaded with author Yudhijit
against time to collect data about Telegram on the Web encouraging observers
into a database, where they would Bhattacharjee (http:// the phenomenon. And so, within around the world to follow up on the object,
be scanned by software designed scim.ag/pod_6115). minutes of finding the object that which the researchers would later label “the
to identify potentially interesting he had labeled PTF11kly, Nugent supernova of a generation” and “an instant
events such as a gamma ray burst. Shortly after instant-messaged another colleague named cosmic classic.”
noon, when the pipeline had been restored and Mark Sullivan at the University of Oxford Nugent had already called a colleague at
all the images uploaded and analyzed, Nugent in the United Kingdom, asking if Sullivan UC Berkeley—a quiet, 42-year-old astro-
sat down to see what the system had picked could arrange for a telescope to start observ- physicist named Weidong Li—to start look-
from the previous night’s observations as can- ing the object immediately. ing at archival images of the Pinwheel galaxy
didates worthy of follow-up. He knew that Luckily, Sullivan was still in his office in an effort to determine the supernova’s pro-
his buddy, Joshua Bloom, was likely doing even though the local time was past 9 p.m. genitor. Nugent knew that Li’s expertise in
exactly that a few kilometers away at the Uni- “Reckon it’s real?” Sullivan asked, to which astrometry, the measurement of the position
versity of California (UC), Berkeley, where Nugent replied: “It is.” Sullivan e-mailed and motion of stars, would be instrumental
Bloom is an associate professor of astronomy. operators of the Liverpool Telescope, a in tracing SN 2011fe’s history. Over the next
Bloom—who had helped write the soft- 2-meter-diameter robotic instrument on La several weeks, Nugent, Bloom, and Li would
ware for the automated search—was in Palma in the Canary Islands off the coast devote themselves night and day to studying
fact looking through the top picks of the of Spain. Within an hour, the telescope had the supernova’s present and past.
22 4 JANUARY 2013 VOL 339 SCIENCE www.sciencemag.org
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2. NEWSFOCUS
Along with the work of dozens of others, Astronomers had been conducting such
the efforts of these three researchers would automated surveys for more than a decade, but
lead to a new understanding of how type Ias Bloom wanted to take them a step further. Until
originate and unfold. But not all three would then, automated searches—such as the one
be around to celebrate the insights gained that Li was in charge of at Mount Hamilton—
from SN 2011fe, which would end up gen- used computers to schedule observations,
erating dozens of research papers. Months control the telescope, and scan images of the
later, one of their lives would come to a tragic sky for possible new supernovae or gamma
and unexpected end. ray bursts by comparing the images with older
reference images. A human being, however,
Core compression still had to inspect each candidate to deter-
Nugent, Bloom, and Li had known each mine whether it was a real astrophysical object
other for several years before SN 2011fe lit or something spurious like a speckle.
up the sky. They had come to astronomy by Bloom and his colleagues developed
very different paths. algorithms to distinguish between fake and
Nugent, the son of a lawyer, got hooked real candidates and to determine what kind
on space as a kid following NASA’s lunar of object a candidate might be: a gamma
Downloaded from www.sciencemag.org on January 4, 2013
program. His interest turned to astronomy ray burst, a nova, a variable star, or some-
when his grandfather gave him a telescope thing else. By inspecting various features of
at the age of 12. In college, he briefly consid- Partners in discovery. Peter Nugent (left) and Joshua a candidate—such as its brightness and the
ered becoming an English major but hated Bloom—and many others—followed SN 2011fe brightness of its host galaxy—the algorithms
rewriting, so he chose physics instead. Later, for months. could make a probabilistic statement about the
while exploring graduate schools, he ran into candidate, for example, classifying it as a
David Branch—a supernova expert at the Nugent met Li not long after he arrived at supernova with 80% probability. The algo-
University of Oklahoma—who quickly con- Berkeley, at a meeting of Filippenko’s research rithms, called Realbogus and Oarical, gave
vinced him that supernovae were the most group, where Li passed around sweets he’d PTF the ability to sift through several kilo-
interesting things to study in astronomy. In brought from China. Nugent didn’t care for bytes of astronomical data within hours and
1996, he joined Lawrence Berkeley National the sweets (“Bean paste is still bean paste,” classify thousands of new candidates from
Laboratory for a postdoctoral fellowship that he would later joke) but was impressed by the every night’s observations.
turned into a staff position. smiling and soft-spoken Li.
Li’s beginnings were a world apart from Within months, Li had the Lick search Explosion
Nugent’s. Born to a farming couple in a Chi- up and running. The very next year, the sur- Death comes to mortals and stars alike. For
nese mountain village, he was the first person vey yielded a rich haul of 20 nearby super- stars that end as supernovae, however, it
in his district to go to college. Like Nugent, novae, marking the beginning of what was brings ultimate glory: a flash of splendor often
he became fascinated by supernovae, which to become a consistently productive run. Li’s more brilliant than the combined brightness
he would later describe as “the glorious role became pivotal to Filippenko’s group. of an entire galaxy. Type Ia supernovae like
explosive stage of stellar “If Weidong were to be run the one that set astronomers’ hearts racing on
evolution.” After earning over by a truck,” Filippenko 24 August 2011, make up a special class of
his doctorate from Beijing would remark at confer- such stellar explosions. What makes them
Normal University in 1995, ences, “my whole group special is that all of them produce nearly the
Li began working at the Bei- would fall apart.” same brightness.
jing Astronomical Observa- The youngest of the Astronomers think type Ias arise in binary
tory, where he set up China’s three—Bloom—came to star systems in which a small, dense star
first systematic supernovae UC Berkeley as an assis- known as a white dwarf has been steadily
search using a telescope at tant professor in 2005 after accumulating material dumped onto it by a
CREDITS (TOP TO BOTTOM): Y. BHATTACHARJEE/SCIENCE; ALEX FILIPPENKO
the observatory’s Xinglong getting a Ph.D. from the companion star. If the white dwarf happens to
station. Within a year, the California Institute of Tech- be composed entirely of carbon and oxygen,
survey had found six new nology (Caltech) in Pasa- something extraordinary happens after it has
supernovae, thanks in part to dena with work on gamma gained enough material to approach 1.4 solar
scheduling software that Li ray bursts. He was 30, with masses. The stage is set for a runaway thermo-
had written to specify what Analyze this. Li’s work helped under- sparkling eyes, a blond goa- nuclear reaction in which carbon and oxy-
parts of the sky the telescope stand the supernova’s antecedents. tee, and a knack for deadpan gen atoms fuse into nickel. The nickel decays
should observe when. humor that he deployed to radioactively into cobalt, which then decays
The success brought Li to the attention of spice up his talks and rib colleagues. radioactively to iron, powering the super-
supernova researchers elsewhere, including Bloom and Nugent became friends, and nova’s incandescence.
Alex Filippenko at UC Berkeley, who was in 2008 they began working together on the Although this theoretical model is gener-
looking for somebody to lead a supernova Palomar Transient Factory (PTF)—a project ally accepted, astronomers have been look-
search he was initiating with a robotic tele- led by Bloom’s doctoral adviser at Caltech, ing for empirical evidence to confirm many
scope at Lick Observatory in Mount Hamil- Shrinivas Kulkarni. The project was an auto- of the details. A fundamental question about
ton, California. In 1997, Filippenko hired Li mated search for transient phenomena includ- the progenitor system is whether the star that
as a postdoc. ing gamma ray bursts and supernovae. explodes is indeed a carbon-oxygen white
www.sciencemag.org SCIENCE VOL 339 4 JANUARY 2013 23
Published by AAAS

3. NEWSFOCUS
dwarf. Another question is what kind of star But Li’s scrutiny of archival images of the gal- remained undetectable for so long, Bloom
the companion has to be in order for the axy found no such star near where the super- and his colleagues calculated, the exploding
exploding star to result in a type Ia. nova was now blazing, effectively ruling out a star must have been at most 2% the diameter
Those questions were on the minds of red giant as the companion. of the sun—a white dwarf.
Nugent and his colleagues on the afternoon Nugent’s calculations agreed. If the com-
of 24 August as SN 2011fe burned in the panion had been a red giant or other large star, Brightness falls
sky, continuing its ascent in brightness. After they showed, the outermost shell of material Through the fall, SN 2011fe dropped in
calling Li—who began looking at archived ejected by the supernova would have slammed brightness as its nickel decayed to cobalt, and
images of the Pinwheel galaxy—Nugent sent into that star within a day or so of the explo- its cobalt to iron. As December approached,
a text message to Caltech astronomer Richard sion. Because telescopes had seen no sign of Nugent, Bloom, and Li e-mailed back and
Ellis urging him to start observing the super- such a collision, Nugent and others concluded forth to finalize press releases their insti-
nova with the Hubble Space Telescope. But that the companion star had been considerably tutions were drafting to announce the two
Nature papers, which were due out in the jour-
Remote. The PIRATE observatory on Mallorca island
nal’s 15 December issue.
provided key evidence for determining the star In the second week of December, Nugent
system that gave rise to SN 2011fe. flew to Stockholm to participate in the festivi-
ties related to the Nobel prizes. Several astron-
Downloaded from www.sciencemag.org on January 4, 2013
omers, including Nugent and Filippenko, had
been invited to celebrate the physics Nobel,
which was being awarded for the discovery
of the accelerating universe. In some sense,
the prize was a celebration of type Ia super-
novae, whose usefulness in measuring cosmic
distances was the foundation of the discovery.
On the evening of 12 December,
Filippenko returned to his hotel room after
dinner and checked his e-mail. Among the
dozens of messages in his inbox was one from
Li. The subject line said: farewell. Filippenko,
who had always worried about losing Li to
a competing research group, clicked on the
the Hubble was booked; observations had to smaller than a red giant—probably a star of message with trepidation.
wait a few days until it became free. sunlike size still in the middle of its life. “Dear Alex,” the message began. “Please
As the sun was setting over the West Coast, For the next 2 weeks, as SN 2011fe got find a seat to sit down before reading this
Nugent drove to the astronomy department on brighter in the sky, Li and Nugent burned email. I am sure you will be shocked beyond
the UC Berkeley campus and walked down to the midnight oil to prepare their results for belief. By now, I should have already com-
a room in the building’s basement from where publication. By 9 September, a day before mitted suicide.”
astronomers can conduct remote observa- the supernova reached peak brightness— Stunned, Filippenko called Berkeley,
tions at Lick Observatory and the Keck tele- allowing thousands of amateur astronomers where it was midafternoon. It was too late, he
scopes at Mauna Kea in Hawaii. A couple of to view it with backyard telescopes—both learned. Li had already killed himself.
Filippenko’s students were at the controls Li and Nugent had submitted their papers to In his suicide note, Li indicated that he
of the Lick Observatory. Geoff Marcy, the Nature. Adam Riess, an astronomer at Johns had taken his life because of a personal fam-
planet-hunting Berkeley astronomer, and a Hopkins University in Baltimore, Maryland, ily difficulty. Li apologized to Bloom and
student were preparing to use one of the Keck who years earlier had lost a lopsided game of Nugent for the inconvenient timing of his
instruments. Drop everything, Nugent told table tennis to Li at Berkeley, sent Li a con- death—days before the publication of the
them: “You need to observe this at Lick— gratulatory note: “I’ll bet no one has sub- Nature papers. Li’s cell phone number was
and you need to observe this at Keck.” For mitted a paper on a supernova by the time it on the embargoed press releases issued the
the next several hours, both telescopes held reached peak! You are even faster in your sci- week before; reporters had been calling Li’s
SN 2011fe in their gaze, obtaining spectra. ence work than in ping pong! I am in awe.” number without getting a response.
The days that followed turned into a blur Three days later, Bloom learned of a piece Nugent had just returned to Berkeley from
for Nugent, Li, and Bloom as they analyzed of data that would help confirm the nature Stockholm and was pulling into his driveway
data pouring in from various telescopes on of the supernova’s progenitor. A 0.4-meter- when he got Filippenko’s e-mail bearing the
CREDIT: SHRIPATHI HADIGAL, PIRATE TEAM
the ground and in space. In the spectrum of diameter robotic telescope on the Mediter- sad news. Bloom got the message sitting in a
the supernova, Nugent found the signatures ranean island of Mallorca had imaged the hotel room in Hong Kong.
of carbon and oxygen, suggesting that the Pinwheel galaxy on the same night that the Devastated, they combed through months
exploding star was a carbon-oxygen white supernova was detected, some 7.5 hours of their e-mail exchanges with Li, looking
dwarf as models predicted. According to one before the detection was made at Palomar. for clues to depression that they might have
leading model, the companion star should The images from Mallorca showed no super- picked up on. They found nothing. Li’s death
have been a red giant—a large, bloated star nova in the patch of sky where the star had would likely remain a mystery to them. All
nearing the end of its life, with a reddish enve- exploded, even though 4 hours had elapsed they knew for certain was that a shining star
lope and a relatively cool surface temperature. since the moment of explosion. To have had dimmed. –YUDHIJIT BHATTACHARJEE
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