Fermi gamma-ray image updates 'extreme Universe' view
The full sky is seen in the map from the
Fermi telescope; gamma-ray sources abound along the galactic plane
(central bar) but are scattered throughout the cosmos
The
Fermi space telescope has yielded the most detailed gamma ray map of
the sky - representing the Universe's most violent and extreme
processes.
The telescope's newest results, as well as the map, were described at the Third Fermi Symposium in Rome this week.
Gamma rays are the highest-energy light we know of, many millions of times more energetic than visible light.
The Fermi collaboration will soon release a full catalogue of all the gamma ray sources discovered so far.
The space telescope was launched in 2008, and the Rome
meeting gathered together the hundreds of scientists who worked with the
data it produces.
Every three hours, the telescope gathers up a full scan of
the sky, spitting out 40 million bits of information each second that it
beams back to the Earth.
FERMI SPACE TELESCOPE
- Telescope has initial 5-year mission, but expected to last for a decade
- Looks at the Universe in highest-energy form of light - gamma rays
- Spacecraft is 2.8m (9.2ft) high and 2.4m (8.2ft) in diameter
- Mission is a team-up between Nasa and US Department of Energy
One of its two instruments, the
Large Area Telescope (Fermi-Lat), has already identified some 1,400
gamma ray sources - a number that will jump significantly with the
publication of the next catalogue.
Meanwhile, its Gamma Ray Burst Monitor has caught hundreds of
the bursts - occasional outpourings of gamma ray energy that can
release in hours more energy than our Sun will ever produce.
"When you look at the Universe with gamma-ray eyes what
you're seeing is the 'extreme Universe'," said Julie McEnery, Fermi
project scientist.
"You're looking at things where there's enormous
acceleration, enormous energy. We see neutron stars, we see supermassive
black holes, we see particles moving at close to the speed of light
smashing into gas in our galaxy," she told BBC News.
One topic of discussion at the meeting is the classification
of various gamma ray sources. These can be so-called active galactic
nuclei whose centres can contain black holes that spew out threads of
gamma rays, sometimes pointing at the Earth.
Similarly, they can be pulsars, the rapidly spinning neutron stars that rhythmically flash their radiation toward the Earth.
"We've seen a lot of what we expected to see, and some things we didn't expect to see," Dr McEnery said.
"We didn't expect that we'd see as many pulsars shining only
in gamma rays, and we've been stunned to discover dozens of millisecond
pulsars, that's been really astounding.
"And in some cases we haven't seen things we did expect to
see, and that's interesting too. For example we haven't seen clusters of
galaxies; you'd expect them to be gamma ray sources and by not seeing
them, that means that some of the ideas people had about high-energy
particles in galaxy clusters must not be true."
“The biggest things and the smallest things in the Universe are neatly tied together in surprising ways”
End Quote
Steven Ritz
Fermi-Lat deputy principal investigator
But lurking among the data Fermi
has collected is the promise of new physics - there are certainly
unidentified gamma ray sources that may represent new kinds of celestial
objects.
And yet to come may be hints of the dark matter that is believed to make up the majority of the mass of the Universe.
"Dark matter is an excellent example of the kind of new
physics that Fermi is sensitive to," said Steven Ritz, deputy principal
investigator for Fermi-Lat.
"We know it must be a form of matter that is unlike the stuff
we know about in our theories of particle physics - it must have
different properties," he explained to BBC News.
"Theories that go beyond what we currently see tend very
neatly to predict the existence of particles that... when they meet each
other can undergo a process that generates gamma rays."
Dr Ritz said that such "indirect" dark matter detections in
far-flung parts of the cosmos could complement the kind of searches for
never-before-seen particles that are going on at facilities such as the
Large Hadron Collider.
In fact, the motions of charged particles in extreme magnetic
fields that give rise to many of the gamma rays that Fermi sees are
just like particle accelerators.
"It's one of the things I like about this field - the biggest
things and the smallest things in the Universe are neatly tied together
in surprising ways."
'Youthful exuberance'
Active galactic nuclei are the most common Fermi gamma-ray sources
Fermi can lend its expert view to physics closer to home;
several presentations at the meeting focused on gamma rays from the Sun
that could shed light on events such as solar flares and coronal mass
ejections.
The shock wave that propagates outward from the Sun during
such outbursts can also accelerate particles that can potentially
endanger satellites and astronauts - but the details of such processes
remain poorly understood.
"The point with Fermi is that it's so sensitive it's likely
going to pick up events never seen before," said Gerald Share, a
high-energy astrophysicist from the University of Maryland.
"It's just opening up a whole new window to monitor the
flares and solar energetic particles at a weaker level than we normally
see," he told BBC News.
What is clear is that the scientists working on the project believe that the best is yet to come from Fermi.
"I think we're entering an adolescence," said Dr Ritz. "We've
had a youthful exuberance, and it's been a fantastic time - a
tremendous amount of new results, hundreds of papers, more productive
than we had hoped.
"I think the next period is one of increased depth where
we'll be working hard to pull out even more interesting signals and more
challenging analyses, and that just comes with more data and a better
understanding of the instrument."