In our Special Topic on gamma-ray burst (GRB) research
over the past decade, Dr. Joshua Bloom's work ranks at #10
by total cites, based on 85 papers cited a total of 3,639
times. Five of these papers are on the lists of the 20
most-cited papers over the past decade and over the past
Dr. Bloom is an Associate Professor in the Astronomy Department at the
University of California, Berkeley. He is also the Principal Investigator
for both the Peters Automated Infrared Imaging Telescope (PAIRITEL) Project
and the Synoptic All-Sky IR Imaging (SASIR) Survey, as well as the Chair of
both the GRB Science Working Group for EXIST and the Keck Observatory
Time-Domain Working Group.
Below, he talks with
ScienceWatch.com about his highly cited GRB
Would you tell us a bit about your
educational background and research experiences?
In the summer of 1994, I went to work with Ed Fenimore at Los Alamos
National Laboratory for my first research project. With astronomy, and with
Dr. Fenimore in particular, it's very easy for a young person to catch the
research bug: it's a wonderfully vast physical science that we know so
little about, and Ed made the challenge of forefront research accessible
As an undergraduate at Harvard, I then worked with Josh Grindlay and won a
prize for my senior thesis research on gamma-ray bursts and X-ray binaries
(that paid for my backpacking in Europe that summer!). On a Herschel Smith
Fellowship from Harvard, I spent one year in Cambridge, England, doing a
research M.Phil. (like a Master's) degree with
Prof. Martin Rees, Ralph Wijers, and Nial Tanvir. In
1997, I started as a graduate at Caltech and began the gamma-ray burst
program with Prof. Shri Kulkarni. Those were rather heady days as the
revolutions in the gamma-ray burst field seemed to come with unflinching
of a gamma-ray burst
In the seconds after it
first pointed at GRB
After the Swift
satellite recorded a
gamma-ray burst near
After getting my Ph.D. in 2002, I took a position in the Society of Fellows
at Harvard until 2005, when I started in a junior faculty position at UC
Berkeley. At Berkeley, I've grown my own small group of students and
postdocs working on gamma-ray bursts and related fields. In 2008, I was
named associate professor with tenure and in 2009 I was named winner of the
Newton Lacy Pierce Prize by the American Astronomical Society.
What first drew your interest to gamma-ray
When I first started thinking about GRBs, we knew very little about where
they came from, what made them, and what would be their importance for the
totality of astrophysics. I was drawn to the sheer mystery of the events
(how far away where they? how much energy did they release?) and, by
extension, the detective work that would need to be applied to unravel
those mysteries. It became easy to stay hooked on the events as the mystery
unraveled and new questions came up; indeed, just as the GRB field seems to
stagnate, a series of discoveries and insights always seem to come along to
re-energize the field—this doesn't happen with most fields in
One of your most-cited papers in our analysis is
the 1999 Nature paper, "The unusual afterglow of the
gamma-ray burst of 26 March 1998 as evidence for a supernova
connection." Would you tell us about this paper, and why you think
it's so highly cited?
Prof. Kulkarni and I went to the Keck telescopes in late 1998 intending to
get some better images of the host galaxy of that event. At the time we
thought that the host had been imaged by us and others about one month
after the event. So it came as a shock that we didn't detect the host in
those late times (galaxies don't disappear after all!). We immediately knew
that those month-after images and spectra were something unseen previously.
We surmised it was evidence for a supernova (SN) but needed to do some
careful reanalysis of all the data to be able to make the best sense of
what had happened.
I presented the first results of this in March 1999 in a conference in
Santa Barbara in the form of a poster. Many of the big names in GRBs were
there and I was very despondent when our claim wasn't at all well received.
Indeed a few were openly against the idea of this being evidence for a SN
concurrent with a GRB (at the time, most believed that GRBs wouldn't be due
to the death of massive stars—as was the implication of my
work—but instead due to mergers of neutron stars).
We had a long referee process for that paper in the spring of 1999 but
after the paper came out, the case was more solid than it had been at the
conference in Santa Barbara. While GRB 980425 at very low redshift had an
obvious SN counterpart (1998bw), 980326 became accepted as the first GRB at
"cosmological" distances associated with a GRB. Many events since then have
had much better evidence for a SN association (the best with spectroscopy
showing this unambiguously), but our paper helped to start the community on
the right track for these events.
This year, you were the first author on the January
Astrophysical Journal paper, "Observations of the naked-eye
GRB 080319B: Implications of nature's brightest explosion." Could you
tell our readers something about this paper?
GRB 080319B was the brightest GRB ever recorded in visible light and the
most distant object that could have been visible to the unaided ("naked")
eye. The event blinded ("saturated"), for several minutes, the detectors of
our 1.3-meter robotic telescope that had started observing the field 52
seconds after the event. This had to be the most fun I ever had writing a
paper because I got to work with so many of my group so closely and so
Three days after GRB, my group and I had been planning on a ski trip to the
Lake Tahoe area. Instead of canceling, we decided to go. But instead of
skiing we sat around the cabin writing the paper together! We submitted the
42-page paper just five days after the event and we largely preceded the
same conclusions of many others who wrote papers afterwards.
Still, our take on the event was a bit different than some of the other
groups. We went through the traditional analysis of the afterglow and the
GRB itself, but we focused on comparing the event to all the others with
rapid follow-up to see just how special it was. It turns out that while it
was the brightest (intrinsically, not just as observed) event at visible
light, within about 30 minutes or so it faded to a level consistent with
the average of other events. This has important implications for the study
of GRBs at very high redshift (large distance from us, where very little is
known about the state of the universe then) because it means that many (if
not most) of the observed GRBs at moderate redshifts could be seen to large
distances with small to mid-sized telescopes. Perhaps the moral is that
being small and nimble can be a great asset not just for these relatively
nearby events but also for the more distant ones too.
How has our knowledge of gamma-ray bursts changed
over the past decade?
In 1999 we knew of just a few GRBs and their (large) distances from us. We
now have distances and great data on hundreds of events. In some ways, the
basic picture was confirmed—that GRBs are the brightest events in the
universe and that most of them come from the death of massive stars. While
the basic ideas of the geometry of the explosions seemed to be confirmed
five years ago, I think it's safe to say that Swift has, with an avalanche
of great data, vastly complicated an otherwise tidy theoretical picture. At
best, our understanding of the geometry of the explosions and the actual
mechanisms that produce the light we see is rudimentary.
"Nature, it seems, loves to make
bursts of gamma rays from a large menu of
We've also begun learning of the great diversity of the "progenitors" of
GRBs. It appears that a minority fraction are, after all, produced in the
violent merger of compact objects like
black holes and neutron stars, and it also appears
that neutron stars themselves can make GRBs. There's likely even more
mechanisms out there. Nature, it seems, loves to make bursts of gamma
rays from a large menu of recipes.
Where would you like to take your research on
gamma-ray bursts in the next decade?
We're hoping to start abstracting from the study of the events themselves
(and what makes them) and start using GRBs as a probe of the universe. They
are bright lighthouses which provide a "core sample" through the universe:
much of the study of afterglows is likely to make use of this in new ways.
Exploiting GRBs to study the "dark ages" (redshifts higher than about 7 or
ages in the universe less than ~800 Million years after the Big Bang) is
not a new idea but it's only just now becoming possible on a technical
level. The EXIST mission, which should fly at the end of this decade, will
be a major boon to the discovery and follow-up of these distant events. We
hope to be part of that last frontier in observational cosmology. Last, the
events that create some GRBs are also likely the creators of gravitational
waves—we hope to observe both the GRBs and the gravity wave events to
better understand both phenomena.
What would you tell people looking to understand
the value of gamma-ray bursts?
GRBs are great laboratories for the study of motion and light from the
fastest-moving material we know about in the universe. The event likely
heralds the birth of a black hole, and so there may be clues in GRBs to
understanding the basic physics in and around black holes. GRBs are also
bright signposts to interesting places in the universe, such as where the
first massive stars are born and die and regions of space heavily obscured
from view. As such, they are the key to understanding not just the life
cycles of the most extreme stars in the universe but important figures in
the study of the universe—its past and its
University of California, Berkeley
Berkeley, CA, USA