fermi gamma ray space telescope

Gamma-ray view of the sky

This view of the gamma-ray sky is constructed from one year of Fermi Large Area Telescope (LAT) observations. The blue color includes the extragalactic gamma-ray background. The map shows the rate at which the LAT detects gamma rays with energies above 300 million electron volts – about 120 million times the energy of visible light – from different sky directions. Brighter colors represent higher rates.

Credit: NASA/DOE/Fermi LAT Collaboration

Hubble dates black hole's last big meal

For the supermassive black hole at the center of our Milky Way galaxy, it’s been a long time between dinners. NASA’s Hubble Space Telescope has found that the black hole ate its last big meal about 6 million years ago, when it consumed a large clump of infalling gas. After the meal, the engorged black hole burped out a colossal bubble of gas weighing the equivalent of millions of suns, which now billows above and below our galaxy’s center.

The immense structures, dubbed the Fermi Bubbles, were first discovered in 2010 by NASA’s Fermi Gamma-ray Space Telescope. But recent Hubble observations of the northern bubble have helped astronomers determine a more accurate age for the bubbles and how they came to be.

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Origin of Milky Way's hypothetical dark matter signal may not be so dark

A mysterious gamma-ray glow at the center of the Milky Way is most likely caused by pulsars – the incredibly dense, rapidly spinning cores of collapsed ancient stars that were up to 30 times more massive than the sun. That’s the conclusion of a new analysis by an international team of astrophysicists, including researchers from the Department of Energy’s SLAC National Accelerator Laboratory. The findings cast doubt on previous interpretations of the signal as a potential sign of dark matter – a form of matter that accounts for 85 percent of all matter in the universe but that so far has evaded detection.

“Our study shows that we don’t need dark matter to understand the gamma-ray emissions of our galaxy,” said Mattia Di Mauro from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and SLAC. “Instead, we have identified a population of pulsars in the region around the galactic center, which sheds new light on the formation history of the Milky Way.”

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Txch This Week: Lab-On-A-Chip Gets Big Boost And The Lemon-Shaped Moon

by Annie Epstein

This week on Txchnologist, we felt a tug on our heartstrings when we read about Lyman Connor’s story. After a fall, Connor spent some time in the hospital and met a small boy who had lost his hand. Inspired by the boy’s plight, he set out to make a low-cost, app-controlled bionic hand. The engineering part has been a success. Now he just needs to find the boy again.

A Swiss team is hard at work creating a new way to filter water at the speedy rate of almost a liter per minute. Their personal water treatment technology uses an advanced polymer membrane with nanoscopic pores that block bacteria, viruses and other microbes from passing through. The device screws on to any plastic bottle and can filter 300 liters of contaminated water, one person’s hydration requirements over the course of a year. 

Manufacturing has begun on parts for the world’s largest experimental nuclear fusion reactor, expected to begin operating in 2020. The international project, now estimated to cost around $20 billion to construct, involves cooperation between Europe, the U.S., Russia, Japan, China, South Korea and India. If it works, the reactor is expected to generate 500 megawatts of power, and one gram of hydrogen fuel will generate as much power as eight tons of oil.

Finally, agricultural scientists are making potatoes for Millenials. Using the age-old method of selective plant breeding, researchers are coming out with tubers colored like raspberries and others splashed with purple accents. Move over bland russets, potatoes with flair will be making their way to markets soon.

Now we’re bringing you the news we’ve been following this week in the world of science, technology and innovation.

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Imagine you had superhero vision and could see a whole new world of fascinating phenomena invisible to the human eye. NASA’s Fermi Gamma-ray Space Telescope gives astrophysicists analogous powers. It captures images of the universe in gamma rays, the most energetic form of light.

On April 12, one of the spacecraft’s instruments – the Large Area Telescope (LAT), which was conceived of and assembled at the Department of Energy’s SLAC National Accelerator Laboratory – detected its billionth extraterrestrial gamma ray.

Since gamma rays are often produced in violent processes, their observation sheds light on extreme cosmic environments, such as powerful star explosions, high-speed particle jets spewed out by supermassive black holes, and ultradense neutron stars spinning unimaginably fast. Gamma rays could also be telltale signs of dark matter particles – hypothetical components of invisible dark matter, which accounts for 85 percent of all matter in the universe.

“Since Fermi’s launch in 2008, the LAT has made a number of important discoveries of gamma-ray emissions from exotic sources in our galaxy and beyond,” says Robert Cameron, head of the LAT Instrument Science Operations Center (ISOC) at SLAC. The LAT has already collected hundreds of times more gamma rays than the previous-generation EGRET instrument on NASA’s Compton Gamma-ray Observatory – an advance that has tremendously deepened insights into the production of this energetic radiation.

Enabling Discovery

Among the LAT discoveries are more than 200 pulsars – rapidly rotating, highly magnetized cores of collapsed stars that were up to 30 times more massive than the Sun. Before Fermi’s launch, only seven of these objects were known to emit gamma rays. As pulsars spin around their axis, they emit “beams” of gamma rays like cosmic lighthouses. Many pulsars rotate several hundred times per second – that’s tens of millions times faster than Earth’s rotation.

“Understanding pulsars tells us about the evolution of stars because they are one possible end point in a star’s life,” Cameron says. “The LAT data have led us to totally revise our understanding of how pulsars emit gamma rays.”

The LAT has also shown for the first time that novae – thermonuclear explosions on the surface of stars that have accumulated material from neighboring stars – can emit gamma rays. These data provide new details about the physics of burning stars, which is a crucial process for the synthesis of chemical elements in the universe.

Even more exotic gamma-ray sources detected by the LAT are microquasars. These objects are star-sized analogs of active galactic nuclei, with gas spinning around a black hole at the center. As the black hole devours matter from its surroundings, it ejects jets of charged particles traveling almost as fast as light into space, generating beams of gamma rays in the process.

At a galactic scale, such an ejection mechanism could have produced what is known as the Fermi bubbles – two giant areas above and below the center of the disk of our Milky Way galaxy that shine in gamma rays. Discovered by the LAT in 2010, these bubbles suggest that the supermassive black hole at the center of our galaxy once was more active than it is today.

Researchers also use the LAT to search for signs of dark matter particles in the central regions of the Milky Way and other galaxies. Theories predict that the hypothetical particles would produce gamma rays when they decay or collide and destroy each other.

“With the sensitivity we have achieved with the LAT, we should in principle be able to see such dark matter signatures,” says SLAC’s Seth Digel, who leads the Fermi group at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and SLAC. “But we haven’t found any conclusive signals yet, and so far the LAT data can also be explained with other astrophysical sources.”

Finally, the LAT has explored gamma ray sources closer to home, including gamma rays produced by thunderstorms in Earth’s atmosphere, by solar flares and even by charged particles hitting the surface of the Moon.

Finding Needles in a Haystack

From its location on Fermi at an altitude of 330 miles, the LAT sees 20 percent of the sky at any given time. Every two orbits – each takes about 95 minutes – the instrument collects the data necessary for a gamma-ray map of the entire sky.

But identifying the right signals for the map is a little bit like finding needles in a haystack: For every gamma-ray photon, the LAT sees many more high-energy charged particles, called cosmic rays. Most of these background signals are rejected right away by hardware triggers and software filters in the LAT on Fermi, which reduces the rate of signals from 10,000 to 400 per second.

The remaining data are compressed, transmitted back to Earth and sent to NASA’s Goddard Space Flight Center in Greenbelt, Maryland, where they get separated into three different datasets for the LAT, the GBM (Fermi’s second scientific instrument, which monitors short-lived gamma-ray bursts) and spacecraft data.

The LAT data are transferred to the LAT ISOC at SLAC, where 1,000 computer cores automatically analyze the data stream and filter out even more background signals. 70 percent of all detected gamma rays are from Earth’s atmosphere, leaving only two to three extraterrestrial gamma-ray signals per second out of the 10,000 initial detector events. These data are then sent back to NASA Goddard, where they are made publicly available for further analysis.

“The ISOC receives about 15 deliveries of LAT data throughout the day for a total of 16 gigabytes or three DVDs worth of data every day,” Cameron says. “For each delivery, the entire process – from the time the data leave Fermi to the time the gamma rays get deposited in the public archive – takes about four hours.”

Next year, the Fermi mission will reach its 10-year operations goal. What happens after that will largely depend on funding.

“With no successor mission planned, the LAT is in many ways irreplaceable, particularly for studies of low-energy gamma rays,” Digel says. “The telescope is still going strong after all these years, and there is a lot of science left to be done.”

An important new role for the LAT is to search for gamma-ray sources associated with gravitational wave events. These ripples in space-time occur, for example, when two black holes merge into a single one, as recently observed by the LIGO detector. This opens up the completely new field of gravitational wave astrophysics.

NASA's Fermi mission expands its search for dark matter

Dark matter, the mysterious substance that constitutes most of the material universe, remains as elusive as ever. Although experiments on the ground and in space have yet to find a trace of dark matter, the results are helping scientists rule out some of the many theoretical possibilities. Three studies published earlier this year, using six or more years of data from NASA’s Fermi Gamma-ray Space Telescope, have broadened the mission’s dark matter hunt using some novel approaches.

“We’ve looked for the usual suspects in the usual places and found no solid signals, so we’ve started searching in some creative new ways,” said Julie McEnery, Fermi project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “With these results, Fermi has excluded more candidates, has shown that dark matter can contribute to only a small part of the gamma-ray background beyond our galaxy, the Milky Way, and has produced strong limits for dark matter particles in the second-largest galaxy orbiting it.”

Dark matter neither emits nor absorbs light, primarily interacts with the rest of the universe through gravity, yet accounts for about 80 percent of the matter in the universe. Astronomers see its effects throughout the cosmos – in the rotation of galaxies, in the distortion of light passing through galaxy clusters, and in simulations of the early universe, which require the presence of dark matter to form galaxies at all.

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Gamma rays from galactic center dark matter?

What is creating the gamma rays at the center of our Galaxy? Excitement is building that one answer is elusive dark matter. Over the past few years the orbiting Fermi Gamma-ray Space Telescope has been imaging our Galaxy’s center in gamma-rays. Repeated detailed analyses indicate that the region surrounding the Galactic center seems too bright to be accounted by known gamma-ray sources. A raw image of the Galactic Center region in gamma-rays is shown above on the left, while the image on the right has all known sources subtracted – leaving an unexpected excess. An exciting hypothetical model that seems to fit the excess involves a type of dark matter known as WIMPs, which may be colliding with themselves to create the detected gamma-rays. This hypothesis is controversial, however, and debate and more detailed investigations are ongoing. Finding the nature of dark matter is one of the great quests of modern science, as previously this unusual type of cosmologically pervasive matter has shown itself only through gravitation.

Image credit: T. Daylan et al., Fermi Space Telescope, NASA

NASA’s Fermi makes first gamma-ray study of a gravitational lens

An international team of astronomers, using NASA’s Fermi observatory, has made the first-ever gamma-ray measurements of a gravitational lens, a kind of natural telescope formed when a rare cosmic alignment allows the gravity of a massive object to bend and amplify light from a more distant source.

This accomplishment opens new avenues for research, including a novel way to probe emission regions near supermassive black holes. It may even be possible to find other gravitational lenses with data from the Fermi Gamma-ray Space Telescope.

In September 2012, Fermi’s Large Area Telescope (LAT) detected a series of bright gamma-ray flares from a source known as B0218+357, located 4.35 billion light-years from Earth in the direction of a constellation called Triangulum. These powerful flares, in a known gravitational lens system, provided the key to making the lens measurement.

Astronomers classify B0218+357 as a blazar – a type of active galaxy noted for its intense emissions and unpredictable behavior. At the blazar’s heart is a supersized black hole with a mass millions to billions of times that of the sun. As matter spirals toward the black hole, some of it blasts outward as jets of particles traveling near the speed of light in opposite directions.

The extreme brightness and variability of blazars result from a chance orientation that brings one jet almost directly in line with Earth. Astronomers effectively look down the barrel of the jet, which greatly enhances its apparent emission.

Long before light from B0218+357 reaches us, it passes directly through a face-on spiral galaxy – one very much like our own – about 4 billion light-years away.

The galaxy’s gravity bends the light into different paths, so astronomers see the background blazar as dual images. With just a third of an arcsecond (less than 0.0001 degree) between them, the B0218+357 images hold the record for the smallest separation of any lensed system known.

Video credit: NASA