Einstein@Home volunteers find four cosmic lighthouses in data from NASA's Fermi Gamma-ray Space Telescope
The combination of globally
distributed computing power and innovative analysis methods proves to be
a recipe for success in the search for new pulsars. Scientists from the
Max Planck Institutes for Gravitational Physics and Radio Astronomy
together with international colleagues have now discovered four
gamma-ray pulsars in data from the Fermi space telescope. The
breakthrough came using the distributed computing project Einstein@Home,
which connects more than 200,000 computers from 40,000 participants
around the world to a global supercomputer. The discoveries include
volunteers from Australia, Canada, France, Germany, Japan, and the USA.
All
four gamma-ray pulsars discovered by Einstein@Home lie in the plane of
our Milky Way, as shown in this sky map using data from Fermi's Large
Area Telescope (LAT). The plane is apparent as an area of particularly
intense gamma radiation; brighter colors indicate more intense
radiation. The insets show the four pulsars as point sources. The flags
indicate the nationalities of the Einstein@Home volunteers whose
computers made the discoveries.© Knispel/Pletsch/AEI/NASA/DOE/Fermi LAT Collaboration
Since its launch in 2008, the Fermi satellite has been observing the entire sky in gamma-rays. It has discovered thousands of previously unknown gamma-ray sources, among which are possibly hundreds of yet undiscovered pulsars – compact and rapidly rotating remnants of exploded stars. Identifying these new gamma-ray pulsars, however, is computationally very expensive – wide parameter ranges have to be “scanned” at very high resolution.
“Our innovative solution for the compute intensive search for
gamma-ray pulsars is the combination of particularly efficient methods
along with the distributed computing power of Einstein@Home,” says
Holger Pletsch, Independent Research Group Leader at the Max Planck
Institute for Gravitational Physics (Albert Einstein Institute/AEI), and
lead author of the study. “The volunteers from around the world enable
us to deal with the huge computational challenge posed by the Fermi data analysis. In this way, they provide an invaluable service to astronomy,” says Pletsch.
Distributed Computing for Astronomy
Einstein@Home is a joint project of the Center for Gravitation and Cosmology at the University of Wisconsin–Milwaukee and the AEI in Hannover. It is funded by the National Science Foundation and the Max Planck Society. Since mid-2011, Einstein@Home has been searching for signals from gamma-ray pulsars in Fermi data. The project was founded in 2005 to search for gravitational-wave signals in data from the LIGO detectors – still the main task of Einstein@Home. Since early 2009, the project has also been conducting successful searches for new radio pulsars.
“The first-time discovery of gamma-ray pulsars by Einstein@Home is a milestone – not only for us but also for our project volunteers. It shows that everyone with a computer can contribute to cutting-edge science and make astronomical discoveries,“ says co-author Bruce Allen, director at the AEI and principal investigator of Einstein@Home. “I'm hoping that our enthusiasm will inspire more people to help us with making further discoveries.”
Using
his home computer, Hans-Peter Tobler from Rellingen, Germany,
discovered one of the four new pulsars. With hundreds of thousands of
computers teaming up, he never expected that his PC would discover
anything. © Hans-Peter Tobler
Pulsars for everyone
The volunteers who contributed to the discoveries are thrilled. “At first I was a bit dumbfounded and thought someone was playing a hoax on me. But after I did some research everything checked out. That someone as insignificant as myself could make a difference was amazing,” says Thomas M. Jackson from Kentucky in the USA, who runs Einstein@Home on his quad-core processor.
The volunteers who contributed to the discoveries are thrilled. “At first I was a bit dumbfounded and thought someone was playing a hoax on me. But after I did some research everything checked out. That someone as insignificant as myself could make a difference was amazing,” says Thomas M. Jackson from Kentucky in the USA, who runs Einstein@Home on his quad-core processor.
Hans-Peter Tobler from Rellingen, Germany, has been participating in
Einstein@Home since 2005 and has now helped in the discovery of a
gamma-ray pulsar: “I'm fascinated by astronomy. Einstein@Home allows me
to contribute to this field of science, even though I'm not a
professional astronomer myself.” With hundreds of thousands of computers
teaming up, he never expected that his PC would discover anything.
All Einstein@Home volunteers are acknowledged for their contributions
in the scientific publication. The astronomers particularly mention the
eight volunteers whose computers made the discoveries. The volunteers
are from Australia, Canada, France, Germany, Japan, and the USA. As a
token of appreciation, they receive special certificates of discovery.
New Window for the Discovery of Neutron Stars
Not only are the four gamma-ray pulsars the first to be found with a distributed volunteer computing project, but also the pulsars are special, too. “It is exciting that all four pulsars are in the plane of our Milky Way,” says co-author Michael Kramer, director at the Max Planck Institute for Radio Astronomy (MPIfR). Earlier surveys with radio telescopes have been thoroughly searching this part of the sky, but the four new pulsars had remained hidden and only one comparable neutron star had been found.
Not only are the four gamma-ray pulsars the first to be found with a distributed volunteer computing project, but also the pulsars are special, too. “It is exciting that all four pulsars are in the plane of our Milky Way,” says co-author Michael Kramer, director at the Max Planck Institute for Radio Astronomy (MPIfR). Earlier surveys with radio telescopes have been thoroughly searching this part of the sky, but the four new pulsars had remained hidden and only one comparable neutron star had been found.
Apparently, the pulsars are only visible in gamma-rays. The radio and
gamma-ray emission are produced in different regions around the pulsar.
Depending on the orientation of the pulsar, the narrow radio beam might
miss Earth, while the wider beam of gamma-ray photons could be
detectable. Dedicated follow-up observations of all four new discoveries
with the MPIfR's 100-meter Effelsberg radio telescope and the
Australian Parkes Observatory confirm the absence of any detectable
radio emission.
“With the successful blind searches for gamma-ray pulsars, we use a
new window for the discovery of neutron stars,” says Kramer. The new
searches employ methods inspired by gravitational-wave data analysis.
Using these, astronomers around Pletsch discovered all of the eleven
gamma-ray pulsars found in the last three years of blind searches in Fermi data.
A neutron star is the densest object astronomers can observe directly,
crushing half a million times Earth's mass into a sphere about 20
kilometers across. This illustration compares the size of a neutron star
to the area around Hannover, Germany, hometown of the Albert Einstein
Institute Hannover. © NASA's Goddard Space Flight Center
Young Neutron Stars with a Hiccup
Two of the newly discovered pulsars exhibited a sudden change in their otherwise perfectly regular rotation – they suffered a so-called pulsar glitch. During a glitch, the neutron star's rotation suddenly speeds up, then gradually becomes slower and returns to the initial rotation period after a few weeks. “We don't know the exact cause of these glitches yet, but measuring them can provide new insights into the incompletely understood neutron star interior,” says co-author Lucas Guillemot, who worked as a researcher at MPIfR when the discoveries were made and has recently taken up a position at the LPC2E in OrlĂ©ans.
Two of the newly discovered pulsars exhibited a sudden change in their otherwise perfectly regular rotation – they suffered a so-called pulsar glitch. During a glitch, the neutron star's rotation suddenly speeds up, then gradually becomes slower and returns to the initial rotation period after a few weeks. “We don't know the exact cause of these glitches yet, but measuring them can provide new insights into the incompletely understood neutron star interior,” says co-author Lucas Guillemot, who worked as a researcher at MPIfR when the discoveries were made and has recently taken up a position at the LPC2E in OrlĂ©ans.
Glitches mostly happen in newly born pulsars. According to the
measurements of the astronomers, the four pulsars discovered now are
between 30,000 and 60,000 years old – youngsters among neutron stars.
Discovery Potential
In the future, the efficient search methods will become increasingly important, since Fermi
is scheduled to take data for at least another five years. The longer
the measurement time, the weaker the pulsars the scientists can
discover. With increasing measurement time, however, the computational
costs grow quickly. Conventional methods are already too costly at
present, but there is still headroom for the new methods.
“Only our methods will enable efficient blind pulsar searches in Fermi
data in the future. Using the distributed computing power provided by
the Einstein@Home volunteers, we hope to discover gamma-ray pulsars that
are particularly far away or faint,” says Pletsch.
Pulsars
Neutron stars are exotic objects. They
are made up of matter much more densely packed than normal, giving the
entire star a density comparable to an atomic nucleus. The diameter of
our sun would shrink to less than 30 km if it was that dense.
Neutron stars also have extremely strong magnetic fields. Charged
particles accelerated along the field lines emit electromagnetic
radiation in different wavelengths. This radiation is bundled into a
cone along the magnetic field axis. As the neutron star turns about its
rotational axis, the cones of emitted radiation sweep through the sky
like a lighthouse beam because the rotational axis is usually inclined
relative to the magnetic field axis. The neutron star is then visible as
a pulsar. Pulsars rotate with cycles of a few seconds up to only
milliseconds with a precision that makes them the most accurate clocks
in the world.
These cosmic lighthouses were first discovered in
1967 by Jocelyn Bell Burnell and identified as radio pulsars. X-ray and
gamma-ray pulsars are also known to exist today. Even though not all
pulsars are observable in all wavelengths, scientists assume that they
still emit radiation in the entire electromagnetic spectrum. However the
mechanisms which govern radiation emission in different frequency
ranges are not yet completely understood.
Gamma-ray Pulsars and Radio Pulsars
A plausible
explanation could be that lower-energy radio waves are bundled in a
tighter cone at the magnetic poles than high-energy gamma-radiation.
Since radiation is mainly emitted along the surface of the cone and
different wavelengths are emitted in cones with a different spread,
radio waves and gamma waves would leave the neutron star in different
directions. A pulsar might thus become visible as a gamma-ray or radio
pulsar to a distant observer (depending on which cone sweeps across the
observers position). Another model has gamma radiation originating not
in the polar regions of the magnetic field but rather the equatorial
plane where the field lines are disrupted. It is therefore very
important to observe as many pulsars as possible in all wavelengths to
better understand these mechanisms.
Data Analysis
When analyzing data from
gravitational wave detectors, scientists have to rely on very effective
algorithms and high computing power. This is necessary, because a
possible gravitational wave signal would be scarcely stronger than the
background noise at the current measurement accuracy.
The data is analyzed in several steps. First, the astrophysicists
scan large areas of the sky for signals. If there is a conspicuous
signal in one direction, they investigate the vicinity with an algorithm
which has a narrower search grid and thus requires more computing time.
If the signal is confirmed, the scientists analyse its temporal
characteristic and examine whether it can be assigned to a specific
pulsar period, for example. The Hanover scientists have modified the
algorithm to search for continuous sources of gravitational waves and
used it successfully to search for gamma-ray pulsars in Fermi data.
Einstein@Home
This project for distributed
volunteer computing connects PC users from all over the world, who
voluntarily donate spare computing time on their home and office
computers. So far more than 350,000 volunteers have participated and it
is therefore one of the largest projects of this kind. Scientific
supporters are the Center for Gravitation and Cosmology at the
University of Wisconsin-Milwaukee and the Max Planck Institute for
Gravitational Physics (Albert Einstein Institute, Hanover) with
financial support from the National Science Foundation and the Max
Planck Society. Since 2005, Einstein@Home has examined data from the
gravitational wave detectors within the LIGO-Virgo-Science Collaboration
(LVC) for gravitational waves from unknown, rapidly rotating neutron
stars.
As of March 2009, Einstein@Home has also been involved in the search
for signals from radio pulsars in observational data from the Arecibo
Observatory in Puerto Rico and the Parkes Observatory in Australia.
Since the first discovery of a radio pulsar by Einstein@Home in August 2010, the global computer network has discovered more than 50 new radio pulsars.
Since the first discovery of a radio pulsar by Einstein@Home in August 2010, the global computer network has discovered more than 50 new radio pulsars.
A new search for gamma-ray pulsars in data of the Fermi
satellite was added in August 2011. It made the four discoveries
reported now. The project is looking for, among other things, the first
millisecond pulsar, visible only in the gamma-ray range.
Science Contacts
Homepage Holger J. Pletsch
Homepage of Bruce Allen
Media Contacts
Science Contacts
Dr. Holger J. Pletsch
Independent Research Group Leader
Phone:+49 511 762-17171Fax:+49 511 762-2784
Email: holger.pletsch@aei.mpg.de
Homepage Holger J. Pletsch
Prof. Dr. Bruce Allen
Director
Phone:+49 511 762-17148Fax:+49 511 762-17182
Email: bruce.allen@aei.mpg.de
Homepage of Bruce Allen
Media Contacts
Dr. Benjamin Knispel
Press Officer AEI Hannover
Phone:+49 511 762-19104Fax:+49 511 762-17182
Email: benjamin.knispel@aei.mpg.de
Dr. Norbert Junkes
Press Officer MPIfR
Phone:+49 228 525-399Fax:+49 228 525-438
Email: njunkes@mpifr-bonn.mpg.de
