Andrew Yee
December 21st 05, 10:03 PM
Research Communications
Ohio State University
Contact:
John Beacom, (614) 247-8102; Beacom.7 @ osu.edu
Written by:
Pam Frost Gorder, (614) 292-9475
12/19/05
WANTED: AMATEUR STARGAZERS TO HELP SOLVE SUPERNOVA MYSTERY
COLUMBUS, Ohio -- Ohio State University scientists have thought of a new
way to solve an astronomical mystery, and their plan relies on a
well-connected network of amateur stargazers and one very elusive
subatomic particle.
To understand what happens inside exploding stars, or supernovae,
scientists need to study particles called neutrinos, explained John
Beacom, assistant professor of physics and astronomy at Ohio State.
Neutrinos are formed in the nuclear reactions that make stars like our sun
shine. Exploding stars overflow with the particles, and flood the universe
with them.
Neutrinos should be everywhere, but they are very hard to detect -- so
hard to detect, in fact, that even though countless neutrinos burrow
through our planet every second, scientists only capture a few of them
each day.
Scientists know that most neutrinos they do detect probably come from our
own Sun, from nuclear reactors in terrestrial power plants, or from cosmic
radiation interacting with our atmosphere. There has been no way to
distinguish whether a particular neutrino came from elsewhere, until now.
That's why Beacom and his team's discovery -- that each year, one or two
of the neutrinos detected on Earth can probably be matched to the
exploding star that made them -- represents a major step forward for
supernova astrophysics.
The discovery also comes at a special time, Beacom said. The method will
fully exploit the capabilities of the next generation of neutrino
detectors, which are now being planned, and take advantage of a growing
number of amateur astronomers who are capable of discovering supernovae.
For a study appearing in a recent issue of the journal Physical Review
Letters, Beacom and his coauthors developed a kind of litmus test for
finding supernova neutrinos: If a detector on Earth registers two of the
particles within ten seconds, odds are high that they came from a
supernova in a nearby galaxy. Alternatively, if an astronomer -- amateur
or otherwise -- spots a supernova, scientists at neutrino detectors can
look back through their records to see if they captured a neutrino around
that time.
Given that a few supernovae occur in nearby galaxies every year, and given
the sensitivity of neutrino detectors on Earth, they've determined that at
least one of those scenarios -- the two-in-ten-seconds event or the
identification of a supernova neutrino after the fact -- should be able to
happen about once a year.
The professionals need amateur astronomers to help spot new supernovae
fast, so scientists can quickly match captured neutrinos with the
exploding stars that made them.
"Even with all our modern telescopes, the professionals can't look at the
whole sky at once," Beacom said. "But the amateurs are everywhere. With
relatively small telescopes, they can see these nearby supernovae, which
are very bright -- often brighter than their host galaxies."
Here, "relatively small" means smaller than a telescope in an astronomical
observatory, but larger than the average backyard telescope.
Coauthor Hasan Yüksel, a postdoctoral researcher at Ohio State , explained
that many of today's so-called amateur astronomers aren't really so
amateur. "You can think of them more as 'professional amateurs,'" he said.
These are the semi-pro players of the hobby set -- skilled folks who build
custom telescopes. They have day jobs, but they scan the skies at night,
and share their findings with other amateurs over the Internet. Often,
they have ties to professional astronomers. When a major discovery is
made, they know as soon as the professionals do.
Yüksel also pointed out that since 2002, there were at least nine
supernovae identified in galaxies within about 30 million light years (180
trillion miles) of our Milky Way, and more than half of those were
discovered by amateurs.
Surprisingly, the Ohio State physicists got their idea in a "eureka"
moment -- after a discussion with colleagues at the Department of
Astronomy's morning coffee event. This daily review of new journal papers
posted to an online archive (http://arXiv.org) has been going on since the
1990s, and often inspires faculty and students to pursue new lines of
research.
Walking back to their offices after coffee, Yüksel asked Beacom and
visiting scholar Shin'ichiro Ando about a special class of galaxies called
starburst galaxies, in which unusually high numbers of stars are being
born. Wouldn't those galaxies also have large numbers of supernovae?
Wouldn't nearby starburst galaxies be good places to look and find out?
Beacom said that something clicked.
"We realized that maybe it's not totally crazy to look for neutrinos from
supernovae in nearby galaxies," he said.
The three performed detailed calculations about supernova rates in nearby
galaxies, and found that the explosions probably happen more often than
people once thought -- about three times a year. Then they looked at the
rates at which neutrinos are caught in giant underground detectors on
Earth.
Their discovery came down to calculating the odds: it's highly unlikely
that a neutrino detector on Earth would capture two particles within any
10 second interval unless both of those neutrinos came from a supernova --
in fact, the same supernova.
"We were kicking ourselves for not thinking of this before," Beacom said.
He cited Supernova 1987A, which occurred in a galaxy that is a very close
companion to the Milky Way. Because detectors on Earth captured 20
neutrinos in only a few seconds during that event, astronomers knew for
sure that they came from 1987A.
But since then?
"A big fat zero," he said. "What if using this technique, we could have
been identifying one additional supernova neutrino per year? By now, we
would have collected a sample as big as that burst in 1987." With the much
larger neutrino detectors that are now being devised, and with the large
number of supernovae that are being spotted these days, it could be done.
Galaxies up to 200 times farther away than the one that spawned Supernova
1987A are still considered near by astronomical standards, and amateurs
would be able to spot supernovae in them. Those galaxies may give us only
one or two neutrinos per year, but that's still more than scientists would
be able to study otherwise.
"These are somewhat desperate measures," Ando admitted. "Why are we so
desperate? Since a supernova expends 99 percent of its energy in
neutrinos, those neutrinos tell the story of how the explosion works, and
therefore we have to find them." Supernova neutrinos are everywhere, but
the vastness of space keeps them hidden.
So, at least a thousand years after people first noticed supernovae in the
skies, what's happening inside these exploding stars is still a mystery.
When scientists simulate supernovae on computer, something always goes
wrong. The explosion starts, and then it fizzles.
"If we can't make a supernova blow up on the computer, that means we're
missing something. We need clues. We need to find those neutrinos," Ando
continued.
Beacom envisions that scientists at neutrino detectors could sound an
alarm whenever they detect two particles in ten seconds. Since supernovae
emit neutrinos at the very start of the explosion, the particles would
reach Earth hours before the supernovae would be visible in telescopes,
and the announcement would amount to a supernova forecast.
Alternatively, when astronomers spot a nearby supernova, they could ask
the scientists at the detectors to look back through their data from
previous hours to find any particle events.
At Beacom's suggestion, scientists working at the Japanese neutrino
detector Super-Kamiokande are going to search their records for events
that could be linked to nearby supernovae in past years.
"While this detector is smaller than those envisioned for the future, it's
been in operation for a decade or two, so it actually stands a good chance
of having detected the first neutrino from an identified supernova beyond
the Milky Way and its closest companions," Beacom said.
Ohio State University
Contact:
John Beacom, (614) 247-8102; Beacom.7 @ osu.edu
Written by:
Pam Frost Gorder, (614) 292-9475
12/19/05
WANTED: AMATEUR STARGAZERS TO HELP SOLVE SUPERNOVA MYSTERY
COLUMBUS, Ohio -- Ohio State University scientists have thought of a new
way to solve an astronomical mystery, and their plan relies on a
well-connected network of amateur stargazers and one very elusive
subatomic particle.
To understand what happens inside exploding stars, or supernovae,
scientists need to study particles called neutrinos, explained John
Beacom, assistant professor of physics and astronomy at Ohio State.
Neutrinos are formed in the nuclear reactions that make stars like our sun
shine. Exploding stars overflow with the particles, and flood the universe
with them.
Neutrinos should be everywhere, but they are very hard to detect -- so
hard to detect, in fact, that even though countless neutrinos burrow
through our planet every second, scientists only capture a few of them
each day.
Scientists know that most neutrinos they do detect probably come from our
own Sun, from nuclear reactors in terrestrial power plants, or from cosmic
radiation interacting with our atmosphere. There has been no way to
distinguish whether a particular neutrino came from elsewhere, until now.
That's why Beacom and his team's discovery -- that each year, one or two
of the neutrinos detected on Earth can probably be matched to the
exploding star that made them -- represents a major step forward for
supernova astrophysics.
The discovery also comes at a special time, Beacom said. The method will
fully exploit the capabilities of the next generation of neutrino
detectors, which are now being planned, and take advantage of a growing
number of amateur astronomers who are capable of discovering supernovae.
For a study appearing in a recent issue of the journal Physical Review
Letters, Beacom and his coauthors developed a kind of litmus test for
finding supernova neutrinos: If a detector on Earth registers two of the
particles within ten seconds, odds are high that they came from a
supernova in a nearby galaxy. Alternatively, if an astronomer -- amateur
or otherwise -- spots a supernova, scientists at neutrino detectors can
look back through their records to see if they captured a neutrino around
that time.
Given that a few supernovae occur in nearby galaxies every year, and given
the sensitivity of neutrino detectors on Earth, they've determined that at
least one of those scenarios -- the two-in-ten-seconds event or the
identification of a supernova neutrino after the fact -- should be able to
happen about once a year.
The professionals need amateur astronomers to help spot new supernovae
fast, so scientists can quickly match captured neutrinos with the
exploding stars that made them.
"Even with all our modern telescopes, the professionals can't look at the
whole sky at once," Beacom said. "But the amateurs are everywhere. With
relatively small telescopes, they can see these nearby supernovae, which
are very bright -- often brighter than their host galaxies."
Here, "relatively small" means smaller than a telescope in an astronomical
observatory, but larger than the average backyard telescope.
Coauthor Hasan Yüksel, a postdoctoral researcher at Ohio State , explained
that many of today's so-called amateur astronomers aren't really so
amateur. "You can think of them more as 'professional amateurs,'" he said.
These are the semi-pro players of the hobby set -- skilled folks who build
custom telescopes. They have day jobs, but they scan the skies at night,
and share their findings with other amateurs over the Internet. Often,
they have ties to professional astronomers. When a major discovery is
made, they know as soon as the professionals do.
Yüksel also pointed out that since 2002, there were at least nine
supernovae identified in galaxies within about 30 million light years (180
trillion miles) of our Milky Way, and more than half of those were
discovered by amateurs.
Surprisingly, the Ohio State physicists got their idea in a "eureka"
moment -- after a discussion with colleagues at the Department of
Astronomy's morning coffee event. This daily review of new journal papers
posted to an online archive (http://arXiv.org) has been going on since the
1990s, and often inspires faculty and students to pursue new lines of
research.
Walking back to their offices after coffee, Yüksel asked Beacom and
visiting scholar Shin'ichiro Ando about a special class of galaxies called
starburst galaxies, in which unusually high numbers of stars are being
born. Wouldn't those galaxies also have large numbers of supernovae?
Wouldn't nearby starburst galaxies be good places to look and find out?
Beacom said that something clicked.
"We realized that maybe it's not totally crazy to look for neutrinos from
supernovae in nearby galaxies," he said.
The three performed detailed calculations about supernova rates in nearby
galaxies, and found that the explosions probably happen more often than
people once thought -- about three times a year. Then they looked at the
rates at which neutrinos are caught in giant underground detectors on
Earth.
Their discovery came down to calculating the odds: it's highly unlikely
that a neutrino detector on Earth would capture two particles within any
10 second interval unless both of those neutrinos came from a supernova --
in fact, the same supernova.
"We were kicking ourselves for not thinking of this before," Beacom said.
He cited Supernova 1987A, which occurred in a galaxy that is a very close
companion to the Milky Way. Because detectors on Earth captured 20
neutrinos in only a few seconds during that event, astronomers knew for
sure that they came from 1987A.
But since then?
"A big fat zero," he said. "What if using this technique, we could have
been identifying one additional supernova neutrino per year? By now, we
would have collected a sample as big as that burst in 1987." With the much
larger neutrino detectors that are now being devised, and with the large
number of supernovae that are being spotted these days, it could be done.
Galaxies up to 200 times farther away than the one that spawned Supernova
1987A are still considered near by astronomical standards, and amateurs
would be able to spot supernovae in them. Those galaxies may give us only
one or two neutrinos per year, but that's still more than scientists would
be able to study otherwise.
"These are somewhat desperate measures," Ando admitted. "Why are we so
desperate? Since a supernova expends 99 percent of its energy in
neutrinos, those neutrinos tell the story of how the explosion works, and
therefore we have to find them." Supernova neutrinos are everywhere, but
the vastness of space keeps them hidden.
So, at least a thousand years after people first noticed supernovae in the
skies, what's happening inside these exploding stars is still a mystery.
When scientists simulate supernovae on computer, something always goes
wrong. The explosion starts, and then it fizzles.
"If we can't make a supernova blow up on the computer, that means we're
missing something. We need clues. We need to find those neutrinos," Ando
continued.
Beacom envisions that scientists at neutrino detectors could sound an
alarm whenever they detect two particles in ten seconds. Since supernovae
emit neutrinos at the very start of the explosion, the particles would
reach Earth hours before the supernovae would be visible in telescopes,
and the announcement would amount to a supernova forecast.
Alternatively, when astronomers spot a nearby supernova, they could ask
the scientists at the detectors to look back through their data from
previous hours to find any particle events.
At Beacom's suggestion, scientists working at the Japanese neutrino
detector Super-Kamiokande are going to search their records for events
that could be linked to nearby supernovae in past years.
"While this detector is smaller than those envisioned for the future, it's
been in operation for a decade or two, so it actually stands a good chance
of having detected the first neutrino from an identified supernova beyond
the Milky Way and its closest companions," Beacom said.