Fermi Gamma-ray Space Telescope facts for kids

Quick facts for kids
Fermi Gamma-ray Space Telescope

Names	Gamma-ray Large Area Space Telescope
Mission type	Gamma-ray astronomy
Operator	NASA · U.S. Department of Energy
Website	Fermi.GSFC.NASA.gov
Mission duration	Planned: 5-10 years Elapsed: 16 years, 4 months, 22 days
Spacecraft properties
Manufacturer	General Dynamics
Launch mass	4,303 kg (9,487 lb)
Dimensions	Stowed: 2.8 × 2.5 m (9.2 × 8.2 ft)
Power	1,500 W average
Start of mission
Launch date	11 June 2008, 16:05 (2008-06-11UTC16:05) UTC
Rocket	Delta II 7920-H #333
Launch site	Cape Canaveral SLC-17B
Contractor	United Launch Alliance
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Semi-major axis	6,912.9 km (4,295.5 mi)
Eccentricity	0.001282
Perigee	525.9 km (326.8 mi)
Apogee	543.6 km (337.8 mi)
Inclination	25.58°
Period	95.33 min
RAAN	29.29°
Argument of perigee	131.16°
Mean anomaly	229.00°
Mean motion	15.10 rev/day
Velocity	7.59 km/s (4.72 mi/s)
Epoch	23 February 2016, 04:46:22 UTC

The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts and solar flares.

Fermi, named for high-energy physics pioneer Enrico Fermi, was launched on 11 June 2008 at 16:05 UTC aboard a Delta II 7920-H rocket. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden, becoming the most sensitive gamma-ray telescope on orbit, succeeding INTEGRAL. The project is a recognized CERN experiment (RE7).

Overview

Fermi on Earth, solar arrays folded

Fermi includes two scientific instruments, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM).

• The LAT is an imaging gamma-ray detector (a pair-conversion instrument) which detects photons with energy from about 20 million to about 300 billion electronvolts (20 MeV to 300 GeV), with a field of view of about 20% of the sky; it may be thought of as a sequel to the EGRET instrument on the Compton Gamma Ray Observatory.
• The GBM consists of 14 scintillation detectors (twelve sodium iodide crystals for the 8 keV to 1 MeV range and two bismuth germanate crystals with sensitivity from 150 keV to 30 MeV), and can detect gamma-ray bursts in that energy range across the whole of the sky not occluded by the Earth.

General Dynamics Advanced Information Systems (formerly Spectrum Astro and now Orbital Sciences) in Gilbert, Arizona, designed and built the spacecraft that carries the instruments. It travels in a low, circular orbit with a period of about 95 minutes. Its normal mode of operation maintains its orientation so that the instruments will look away from the Earth, with a "rocking" motion to equalize the coverage of the sky. The view of the instruments will sweep out across most of the sky about 16 times per day. The spacecraft can also maintain an orientation that points to a chosen target.

Both science instruments underwent environmental testing, including vibration, vacuum, and high and low temperatures to ensure that they can withstand the stresses of launch and continue to operate in space. They were integrated with the spacecraft at the General Dynamics ASCENT facility in Gilbert, Arizona.

Data from the instruments are available to the public through the Fermi Science Support Center web site. Software for analyzing the data is also available.

GLAST renamed Fermi Gamma-ray Space Telescope

NASA's Alan Stern, associate administrator for Science at NASA Headquarters, launched a public competition 7 February 2008, closing 31 March 2008, to rename GLAST in a way that would "capture the excitement of GLAST's mission and call attention to gamma-ray and high-energy astronomy ... something memorable to commemorate this spectacular new astronomy mission ... a name that is catchy, easy to say and will help make the satellite and its mission a topic of dinner table and classroom discussion".

Fermi gained its new name in 2008: On 26 August 2008, GLAST was renamed the "Fermi Gamma-ray Space Telescope" in honor of Enrico Fermi, a pioneer in high-energy physics.

Mission

Anticipated first year of operations timeline

Gamma-ray radiation (greater than 1 Gev) detected over the entire sky; brighter areas are more radiation (five year study by Fermi: 2009–2013)

NASA designed the mission with a five-year lifetime, with a goal of ten years of operations.

The key scientific objectives of the Fermi mission have been described as:

• To understand the mechanisms of particle acceleration in active galactic nuclei (AGN), pulsars, and supernova remnants (SNR).
• Resolve the gamma-ray sky: unidentified sources and diffuse emission.
• Determine the high-energy behavior of gamma-ray bursts and transients.
• Probe dark matter (e.g. by looking for an excess of gamma rays from the center of the Milky Way) and early Universe.
• Search for evaporating primordial micro black holes (MBH) from their presumed gamma burst signatures (Hawking Radiation component).

Discoveries

Cycle of pulsed gamma rays from the Vela pulsar, constructed from photons detected by LAT

Pulsar discovery

The first major discovery came when the space telescope detected a pulsar in the CTA 1 supernova remnant that appeared to emit radiation in the gamma ray bands only, a first for its kind. This new pulsar sweeps the Earth every 316.86 milliseconds and is about 4,600 light-years away.

Greatest gamma-ray burst energy release

In September 2008, the gamma-ray burst GRB 080916C in the constellation Carina was recorded by the Fermi telescope. This burst is notable as having "the largest apparent energy release yet measured". The explosion had the power of about 9,000 ordinary supernovae, and the relativistic jet of material ejected in the blast must have moved at a minimum of 99.9999% the speed of light. Overall, GRB 080916C had "the greatest total energy, the fastest motions, and the highest initial-energy emissions" ever seen.

Cosmic rays and supernova remnants

In February 2010, it was announced that Fermi-LAT had determined that supernova remnants act as enormous accelerators for cosmic particles. This determination fulfills one of the stated missions for this project.

Background gamma ray sources

In March 2010 it was announced that active galactic nuclei are not responsible for most gamma-ray background radiation. Though active galactic nuclei do produce some of the gamma-ray radiation detected here on Earth, less than 30% originates from these sources. The search now is to locate the sources for the remaining 70% or so of all gamma-rays detected. Possibilities include star forming galaxies, galactic mergers, and yet-to-be explained dark matter interactions.

Milky Way Gamma- and X-ray emitting Fermi bubbles

Galactic gamma- and X-ray bubbles

Gamma- and X-ray bubbles at the Milky Way galaxy center: Top: illustration; Bottom: video.

In November 2010, it was announced that two gamma-ray and X-ray emitting bubbles were detected around Earth's and the Solar System's host galaxy, the Milky Way. The bubbles, named Fermi bubbles, extend about 25 thousand light-years distant above and below the galactic center. The galaxy's diffuse gamma-ray fog hampered prior observations, but the discovery team led by D. Finkbeiner, building on research by G. Dobler, worked around this problem.

Highest energy light ever seen from the Sun

In early 2012, Fermi/GLAST observed the highest energy light ever seen in a solar eruption.

At the flare's peak, the LAT detected gamma rays with two billion times the energy of visible light, or about four billion electron volts (GeV), easily setting a record for the highest-energy light ever detected during or immediately after a solar flare

—NASA

Terrestrial gamma-ray flash observations

Fermi telescope has observed and detected numerous terrestrial gamma-ray flashes and discovered that such flashes can produce 100 trillion positrons, far more than scientists had previously expected.

GRB 130427A

GRB 130427A before and after in more than 100 MeV light

On 27 April 2013, Fermi detected GRB 130427A, a gamma-ray burst with one of the highest energy outputs yet recorded. This included detection of a gamma-ray over 94 billion electron volts (GeV). This broke Fermi's previous record detection, by over three times the amount.

GRB coincident with gravitational wave event GW150914

Fermi reported that its GBM instrument detected a weak gamma-ray burst above 50 keV, starting 0.4 seconds after the LIGO event and with a positional uncertainty region overlapping that of the LIGO observation. The Fermi team calculated the odds of such an event being the result of a coincidence or noise at 0.22%. However, observations from the INTEGRAL telescope's all-sky SPI-ACS instrument indicated that any energy emission in gamma-rays and hard X-rays from the event was less than one millionth of the energy emitted as gravitational waves, concluding that "this limit excludes the possibility that the event is associated with substantial gamma-ray radiation, directed towards the observer." If the signal observed by the Fermi GBM was associated with GW150914, SPI-ACS would have detected it with a significance of 15 sigma above the background. The AGILE space telescope also did not detect a gamma-ray counterpart of the event. A follow-up analysis of the Fermi report by an independent group, released in June 2016, purported to identify statistical flaws in the initial analysis, concluding that the observation was consistent with a statistical fluctuation or an Earth albedo transient on a 1-second timescale. A rebuttal of this follow-up analysis, however, pointed out that the independent group misrepresented the analysis of the original Fermi GBM Team paper and therefore misconstrued the results of the original analysis. The rebuttal reaffirmed that the false coincidence probability is calculated empirically and is not refuted by the independent analysis.

In October 2018, astronomers reported that GRB 150101B, 1.7 billion light years away from Earth, may be analogous to the historic GW170817. It was detected on 1 January 2015 at 15:23:35 UT by the Gamma-ray Burst Monitor on board the Fermi Gamma-ray Space Telescope, along with detections by the Burst Alert Telescope (BAT) on board the Swift Observatory Satellite.

Black hole mergers of the type thought to have produced the gravitational wave event are not expected to produce gamma-ray bursts, as stellar-mass black hole binaries are not expected to have large amounts of orbiting matter. Avi Loeb has theorised that if a massive star is rapidly rotating, the centrifugal force produced during its collapse will lead to the formation of a rotating bar that breaks into two dense clumps of matter with a dumbbell configuration that becomes a black hole binary, and at the end of the star's collapse it triggers a gamma-ray burst. Loeb suggests that the 0.4 second delay is the time it took the gamma-ray burst to cross the star, relative to the gravitational waves.

GRB 170817A signals a multi-messenger transient

On 17 August 2017, Fermi Gamma-Ray Burst Monitor software detected, classified, and localized a gamma-ray burst which was later designated as GRB 170817A. Six minutes later, a single detector at Hanford LIGO registered a gravitational-wave candidate which was consistent with a binary neutron star merger, occurring 2 seconds before the GRB 170817A event. This observation was "the first joint detection of gravitational and electromagnetic radiation from a single source".

Education and public outreach

Education and public outreach are important components of the Fermi project. The main Fermi education and public outreach website at http://glast.sonoma.edu offers gateways to resources for students, educators, scientists, and the public. NASA's Education and Public Outreach (E/PO) group operates the Fermi education and outreach resources at Sonoma State University.

See also

In Spanish: Telescopio Fermi para niños