Did you know our Milky Way galaxy is blowing
bubbles? Two of them, each 25,000 light-years tall! They extend above and below
the disk of the galaxy, like the two halves of an hourglass. We can’t see them
with our own eyes because they’re only apparent in gamma-ray light, the highest-energy light in the
universe.
We didn’t even know these humongous structures were smack in the middle of
our galaxy until 2010. Scientists found them when they
analyzed the first two years of data from NASA’s Fermi Gamma-ray Space Telescope.
They dubbed them the “Fermi bubbles” and found that in addition to being really
big and spread out, they seem to have well-defined edges. The bubbles’ shape
and the light they give off led scientists to think they were created by a
rapid release of energy. But by what? And when?
One possible explanation is that they could be
leftovers from the last big meal eaten by the supermassive black hole at the
center of our galaxy. This monster is more than 4 million times the mass of our
own Sun. Scientists think it may have slurped up a big cloud of hydrogen
between 6
and 9 million years ago and then burped jets of hot gas
that we see in gamma rays and X-rays.
Another possible explanation is that the bubbles
could be the remains of star formation. There are massive clusters of stars at
very the center of the Milky Way — sometimes the stars are so closely packed they’re a million times more dense than in the outer
suburb of the galaxy where we live. If there was a burst
of star formation in this area a few million years ago, it could have created
the surge of gas needed to in turn create the Fermi bubbles.
It took us until 2010 to see these Fermi bubbles
because the sky is filled with a fog of other gamma rays that can obscure our
view. This fog is created when particles
moving near light speed bump into gas, dust, and light in the Milky Way. These
collisions produce gamma rays, and scientists had to factor out the fog to
unveil the bubbles.
Black holes, cosmic rays, neutron stars and even new kinds of physics — for 10 years, data from our Fermi Gamma-ray Space Telescope have helped unravel some of the biggest mysteries of the cosmos. And Fermi is far from finished!
On June 11, 2008, at Cape Canaveral in Florida, the countdown started for Fermi, which was called the Gamma-ray Large Area Space Telescope (GLAST) at the time.
The telescope was renamed after launch to honor Enrico Fermi, an Italian-American pioneer in high-energy physics who also helped develop the first nuclear reactor.
The Fermi telescope measures some of the highest energy bursts of light in the universe; watching the sky to help scientists answer all sorts of questions about some of the most powerful objects in the universe.
Its main instrument is the Large Area Telescope (LAT), which can view 20% of the sky at a time and makes a new image of the whole gamma-ray sky every three hours. Fermi’s other instrument is the Gamma-ray Burst Monitor. It sees even more of the sky at lower energies and is designed to detect brief flashes of gamma-rays from the cosmos and Earth.
This sky map below is from 2013 and shows all of the high energy gamma rays observed by the LAT during Fermi’s first five years in space. The bright glowing band along the map’s center is our own Milky Way galaxy!
So what are gamma rays?
Well, they’re a form of light. But light with so much energy and with such short wavelengths that we can’t see them with the naked eye. Gamma rays require a ton of energy to produce — from things like subatomic particles (such as protons) smashing into each other.
Here on Earth, you can get them in nuclear reactors and lightning strikes. Here’s a glimpse of the Seattle skyline if you could pop on a pair of gamma-ray goggles. That purple streak? That’s still the Milky Way, which is consistently the brightest source of gamma rays in our sky.
In space, you find that kind of energy in places like black holes and neutron stars. The raindrop-looking animation below shows a big flare of gamma rays that Fermi spotted coming from something called a blazar, which is a kind of quasar, which is different from a pulsar… actually, let’s back this up a little bit.
One of the sources of gamma rays that Fermi spots are pulsars. Pulsars are a kind of neutron star, which is a kind of star that used to be a lot bigger, but collapsed into something that’s smaller and a lot denser. Pulsars send out beams of gamma rays. But the thing about pulsars is that they rotate.
So Fermi only sees a beam of gamma rays from a pulsar when it’s pointed towards Earth. Kind of like how you only periodically see the beam from a lighthouse. These flashes of light are very regular. You could almost set your watch by them!
Quasars are supermassive black holes surrounded by disks of gas. As the gas falls into the black hole, it releases massive amount of energy, including — you guessed it — gamma rays. Blazars are quasars that send out beams of gamma rays and other forms of light — right in our direction.
When Fermi sees them, it’s basically looking straight down this tunnel of light, almost all the way back to the black hole. This means we can learn about the kinds of conditions in that environment when the rays were emitted. Fermi has found about 5,500 individual sources of gamma rays, and the bulk of them have been blazars, which is pretty nifty.
But gamma rays also have many other sources. We’ve seen them coming from supernovas where stars die and from star factories where stars are born. They’re created in lightning storms here on Earth, and our own Sun can toss them out in solar flares.
Fermi has been looking at the sky for almost 10 years now, and it’s helped scientists advance our understanding of the universe in many ways. And the longer it looks, the more we’ll learn. Discover more about how we’ll be celebrating Fermi’s achievements all year.
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Did you know some of the brightest sources of light in the sky come from black holes in the centers of galaxies? It sounds a little contradictory, but it’s true! They may not look bright to our eyes, but satellites have spotted oodles of them across the universe.
One of those satellites is our Fermi Gamma-ray Space Telescope. Fermi has found thousands of these kinds of galaxies in the 10 years it’s been operating, and there are many more out there!
Black holes are regions of space that have so much gravity that nothing - not light, not particles, nada - can escape. Most galaxies have supermassive black holes at their centers - these are black holes that are hundreds of thousands to billions of times the mass of our sun - but active galactic nuclei (also called “AGN” for short, or just “active galaxies”) are surrounded by gas and dust that’s constantly falling into the black hole. As the gas and dust fall, they start to spin and form a disk. Because of the friction and other forces at work, the spinning disk starts to heat up.
The disk’s heat gets emitted as light - but not just wavelengths of it that we can see with our eyes. We see light from AGN across the entire electromagnetic spectrum, from the more familiar radio and optical waves through to the more exotic X-rays and gamma rays, which we need special telescopes to spot.
About one in 10 AGN beam out jets of energetic particles, which are traveling almost as fast as light. Scientists are studying these jets to try to understand how black holes - which pull everything in with their huge amounts of gravity - somehow provide the energy needed to propel the particles in these jets.
Many of the ways we tell one type of AGN from another depend on how they’re oriented from our point of view. With radio galaxies, for example, we see the jets from the side as they’re beaming vast amounts of energy into space. Then there’s blazars, which are a type of AGN that have a jet that is pointed almost directly at Earth, which makes the AGN particularly bright.
Our Fermi Gamma-ray Space Telescope has been searching the sky for gamma ray sources for 10 years. More than half (57%) of the sources it has found have been blazars. Gamma rays are useful because they can tell us a lot about how particles accelerate and how they interact with their environment.
So why do we care about AGN? We know that some AGN formed early in the history of the universe. With their enormous power, they almost certainly affected how the universe changed over time. By discovering how AGN work, we can understand better how the universe came to be the way it is now.
Confused? Don’t be! We get a ton of questions about Fermi and figured we’d take a moment to answer a few of them here.
1. Who was this Fermi guy?
The Fermi telescope was named after Enrico Fermi in recognition of his work on how the tiny particles in space become accelerated by cosmic objects, which is crucial to understanding many of the objects that his namesake satellite studies.
Enrico Fermi was an Italian physicist and Nobel Prize winner (in 1938) who immigrated to the United States to be a professor of physics at Columbia University, later moving to the University of Chicago.
Original image courtesy Argonne National Laboratory
Over the course of his career, Fermi was involved in many scientific endeavors, including the Manhattan Project, quantum theory and nuclear and particle physics. He even engineered the first-ever atomic reactor in an abandoned squash court (squash is the older, English kind of racquetball) at the University of Chicago.
There are a number of other things named after Fermi, too: Fermilab, the Enrico Fermi Nuclear Generating Station, the Enrico Fermi Institute and more. (He’s kind of a big deal in the physics world.)
Fermi even had something to say about aliens! One day at lunch with his buddies, he wondered if extraterrestrial life existed outside our solar system, and if it did, why haven’t we seen it yet? His short conversation with friends sparked decades of research into this idea and has become known as the Fermi Paradox — given the vastness of the universe, there is a high probability that alien civilizations exist out there, so they should have visited us by now.
2. So, does the Fermi telescope look for extraterrestrial life?
Fermi does not look for aliens, extraterrestrial life or anything of the sort! If aliens were to come our way, Fermi would be no help in identifying them, and they might just slip right under Fermi’s nose. Unless, of course, those alien spacecraft were powered by processes that left behind traces of gamma rays.
Fermi detects gamma rays, the highest-energy form of light, which are often produced by events so far away the light can take billions of years to reach Earth. The satellite sees pulsars, active galaxies powered by supermassive black holes and the remnants of exploding stars. These are not your everyday stars, but the heavyweights of the universe.
The LAT sees about one-fifth of the sky at a time and records gamma rays that are millions of times more energetic than visible light. The GBM detects lower-energy emissions, which has helped it identify more than 2,000 gamma-ray bursts – energetic explosions in galaxies extremely far away.
Nope. In movies and comic books, the hero has a tragic backstory and a brush with death, only to rise out of some radioactive accident stronger and more powerful than before. In reality, that much radiation would be lethal.
In fact, as a form of radiation, gamma rays are dangerous for living cells. If you were hit with a huge amount of gamma radiation, it could be deadly — it certainly wouldn’t be the beginning of your superhero career.
5. That sounds bad…does that mean if a gamma-ray burst hit Earth, it would wipe out the planet and destroy us all?
Thankfully, our lovely planet has an amazing protector from gamma radiation: an atmosphere. That is why the Fermi telescope is in orbit; it’s easier to detect gamma rays in space!
Gamma-ray bursts are so far away that they pose no threat to Earth. Fermi sees gamma-ray bursts because the flash of gamma rays they release briefly outshines their entire home galaxies, and can sometimes outshine everything in the gamma-ray sky.
If a habitable planet were too close to one of these explosions, it is possible that the jet emerging from the explosion could wipe out all life on that planet. However, the probability is extremely low that a gamma-ray burst would happen close enough to Earth to cause harm. These events tend to occur in very distant galaxies, so we’re well out of reach.
We hope that this has helped to clear up a few misconceptions about the Fermi Gamma-ray Space Telescope. It’s a fantastic satellite, studying the craziest extragalactic events and looking for clues to unravel the mysteries of our universe!
The Fermi Gamma-ray Space Telescope has been observing some of the most extreme objects and events in the universe — from supermassive black holes to merging neutron stars and thunderstorms — for 10 years. Fermi studies the cosmos using gamma rays, the highest-energy form of light, and has discovered thousands of new phenomena for scientists.
In 2016, Fermi showed the Moon is brighter in gamma rays than the Sun. Because the Moon doesn’t have a magnetic field, the surface is constantly pelted from all directions by cosmic rays. These produce gamma rays when they run into other particles, causing a full-Moon gamma-ray glow.
Many galaxies, including our own, have black holes at their centers. In active galaxies, dust and gas fall into and “feed” the black hole, releasing light and heat. In 2015 for the first time, scientists using Fermi data found hints that a galaxy called PG 1553+113 has a years-long gamma-ray emission cycle. They’re not sure what causes this cycle, but one exciting possibility is that the galaxy has a second supermassive black hole that causes periodic changes in what the first is eating.
Gamma-ray bursts are the most luminous explosions in the universe. In 2013, Fermi spotted the brightest burst it’s seen so far in the constellation Leo. In the first three seconds alone, the burst, called GRB 130427A, was brighter than any other burst seen before it. This record has yet to be shattered.
We can directly observe only 20 percent of the matter in the universe. The rest is invisible to telescopes and is called dark matter — and we’re not quite sure what it is. In 2012, Fermi helped place new limits on the properties of dark matter, essentially narrowing the field of possible particles that can describe what dark matter is.
‘Superflares’ in the Crab Nebula
The Crab Nebula supernova remnant is one of the most-studied targets in the sky — we’ve been looking at it for almost a thousand years! In 2011, Fermi saw it erupt in a flare five times more powerful than any previously seen from the object. Scientists calculate the electrons in this eruption are 100 times more energetic than what we can achieve with particle accelerators on Earth.
Neutron stars have magnetic fields trillions of times stronger than Earth’s. Magnetars are neutron stars with magnetic fields 1,000 times stronger still. In 2009, Fermi saw a storm of gamma-ray bursts from a magnetar called SGR J1550-5418, which scientists think were related to seismic waves rippling across its surface.
A Dark Pulsar
We observe many pulsars using radio waves, visible light or X-rays. In 2008, Fermi found the first gamma-ray only pulsar in a supernova remnant called CTA 1. We think that the “beam” of gamma rays we see from CTA 1 is much wider than the beam of other types of light from that pulsar. Those other beams never sweep across our vision — only the gamma-rays.
A simulated image of NASA’s Nancy Grace Roman Space Telescope’s future observations toward the center of our galaxy, spanning less than 1 percent of the total area of Roman’s Galactic Bulge Time-Domain Survey. The simulated stars were drawn from the Besançon Galactic Model.
Exploring the Changing Universe with the Roman Space Telescope
The view from your backyard might paint the universe as an unchanging realm, where only twinkling stars and nearby objects, like satellites and meteors, stray from the apparent constancy. But stargazing through NASA’s upcoming Nancy Grace Roman Space Telescope will offer a front row seat to a dazzling display of cosmic fireworks sparkling across the sky.
For 10 years, our Fermi Gamma-ray Space Telescope has scanned the sky for gamma-ray bursts (GRBs), the universe’s most luminous explosions!
Most GRBs occur when some types of massive stars run out of fuel and collapse to create new black holes. Others happen when two neutron stars, superdense remnants of stellar explosions, merge. Both kinds of cataclysmic events create jets of particles that move near the speed of light.
A new catalog of the highest-energy blasts provides scientists with fresh insights into how they work. Below are five record-setting events from the catalog that have helped scientists learn more about GRBs:
1. Super-short burst in Boötes!
The short burst 081102B, which occurred in the constellation Boötes on Nov. 2, 2008, is the briefest LAT-detected GRB, lasting just one-tenth of a second!
2. Long-lived burst!
Long-lived burst 160623A, spotted on June 23, 2016, in the constellation Cygnus, kept shining for almost 10 hours at LAT energies — the longest burst in the catalog.
For both long and short bursts, the high-energy gamma-ray emission lasts longer than the low-energy emission and happens later.
3. Highest energy gamma-rays!
The highest-energy individual gamma ray detected by Fermi’s LAT reached 94 billion electron volts (GeV) and traveled 3.8 billion light-years from the constellation Leo. It was emitted by 130427A, which also holds the record for the most gamma rays — 17 — with energies above 10 GeV.
4. In a constellation far, far away!
The farthest known GRB occurred 12.2 billion light-years away in the constellation Carina. Called 080916C, researchers calculate the explosion contained the power of 9,000 supernovae.
5. Probing the physics of our cosmos!
The known distance to 090510 helped test Einstein’s theory that the fabric of space-time is smooth and continuous. Fermi detected both a high-energy and a low-energy gamma ray at nearly the same instant. Having traveled the same distance in the same amount of time, they showed that all light, no matter its energy, moves at the same speed through the vacuum of space.
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Every second, every square meter of Earth’s atmosphere is pelted by thousands of high-energy particles traveling at nearly the speed of light. These zippy little assailants are called cosmic rays, and they’ve been puzzling scientists since they were first discovered in the early 1900s. One of the Fermi Gamma-ray Space Telescope’s top priority missions has been to figure out where they come from.
“Cosmic ray” is a bit of a misnomer. Makes you think they’re light, right? But they aren’t light at all! They’re particles that mostly come from outside our solar system — which means they’re some of the only interstellar matter we can study — although the Sun also produces some. Cosmic rays hit our atmosphere and break down into secondary cosmic rays, most of which disperse quickly in the atmosphere, although a few do make it to Earth’s surface.
Cosmic rays are subatomic particles — smaller particles that make up atoms. Most of them (99%) are nuclei of atoms like hydrogen and helium stripped of their electrons. The other 1% are lone electrons. When cosmic rays run into molecules in our atmosphere, they produce secondary cosmic rays, which include even lighter subatomic particles.
So where do cosmic rays come from? We should just be able to track them back to their source, right? Not exactly. Any time they run into a strong magnetic field on their way to Earth, they get deflected and bounce around like a game of cosmic pinball. So there’s no straight line to follow back to the source. Most of the cosmic rays from a single source don’t even make it to Earth for us to measure. They shoot off in a different direction while they’re pin balling.
Photo courtesy of Argonne National Laboratory
In 1949 Enrico Fermi — an Italian-American physicist, pioneer of high-energy physics and Fermi satellite namesake — suggested that cosmic rays might accelerate to their incredible speeds by ricocheting around inside the magnetic fields of interstellar gas clouds. And in 2013, the Fermi satellite showed that the expanding clouds of dust and gas produced by supernovas are a source of cosmic rays.
When a star explodes in a supernova, it produces a shock wave and rapidly expanding debris. Particles trapped by the supernova remnant magnetic field bounce around wildly.
Every now and then, they cross the shock wave and their energy ratchets up another notch. Eventually they become energetic enough to break free of the magnetic field and zip across space at nearly the speed of light — some of the fastest-traveling matter in the universe.
How can we track them back to supernovas when they don’t travel in a straight line, you ask? Very good question! We use something that does travel in a straight line — gamma rays (actual rays of light this time, on the more energetic end of the electromagnetic spectrum).
When the particles get across the shock wave, they interact with non-cosmic-ray particles in clouds of interstellar gas. Cosmic ray electrons produce gamma rays when they pass close to an atomic nucleus. Cosmic ray protons, on the other hand, produce gamma rays when they run into normal protons and produce another particle called a pion (Just hold on! We’re almost there!) which breaks down into two gamma rays.
The proton- and electron-produced gamma rays are slightly different. Fermi data taken over four years showed that most of the gamma rays coming from some supernova remnants have the energy signatures of cosmic ray protons knocking into normal protons. That means supernova remnants really are powerful particle accelerators, creating a lot of the cosmic rays that we see!
A flash of lightning. A roll of thunder. These are normal stormy sights and sounds. But sometimes, up above the clouds, stranger things happen. Our Fermi Gamma-ray Space Telescope has spotted bursts of gamma rays - some of the highest-energy forms of light in the universe - coming from thunderstorms. Gamma rays are usually found coming from objects with crazy extreme physics like neutron stars and black holes.
So why is Fermi seeing them come from thunderstorms?
Thunderstorms form when warm, damp air near the ground starts to rise and encounters colder air. As the warm air rises, moisture condenses into water droplets. The upward-moving water droplets bump into downward-moving ice crystals, stripping off electrons and creating a static charge in the cloud.
The top of the storm becomes positively charged, and the bottom becomes negatively charged, like two ends of a battery. Eventually the opposite charges build enough to overcome the insulating properties of the surrounding air - and zap! You get lightning.
When those electrons run into air molecules, they emit a terrestrial gamma-ray flash, which means that thunderstorms are creating some of the highest energy forms of light in the universe. But that’s not all - thunderstorms can also produce antimatter! Yep, you read that correctly! Sometimes, a gamma ray will run into an atom and produce an electron and a positron, which is an electron’s antimatter opposite!
The Fermi Gamma-ray Space Telescope can spot terrestrial gamma-ray flashes within 500 miles of the location directly below the spacecraft. It does this using an instrument called the Gamma-ray Burst Monitor which is primarily used to watch for spectacular flashes of gamma rays coming from the universe.
There are an estimated 1,800 thunderstorms occurring on Earth at any given moment. Over the 10 years that Fermi has been in space, it has spotted about 5,000 terrestrial gamma-ray flashes. But scientists estimate that there are 1,000 of these flashes every day - we’re just seeing the ones that are within 500 miles of Fermi’s regular orbits, which don’t cover the U.S. or Europe.
The map above shows all the flashes Fermi has seen since 2008. (Notice there’s a blob missing over the lower part of South America. That’s the South Atlantic Anomaly, a portion of the sky where radiation affects spacecraft and causes data glitches.)
Fermi has also spotted terrestrial gamma-ray flashes coming from individual tropical weather systems. The most productive system we’ve seen was Tropical Storm Julio in 2014, which later became a hurricane. It produced four flashes in just 100 minutes!
How will the James Webb Space Telescope change how we see the universe? Ask an expert!
The James Webb Space Telescope is launching on December 22, 2021. Webb’s revolutionary technology will explore every phase of cosmic history—from within our solar system to the most distant observable galaxies in the early universe, to everything in between. Postdoctoral Research Associate Naomi Rowe-Gurney will be taking your questions about Webb and Webb science in an Answer Time session on Tuesday, December 14 from noon to 1 p.m EST here on our Tumblr!
Dr. Naomi Rowe-Gurney recently completed her PhD at the University of Leicester and is now working at NASA Goddard Space Flight Center as a postdoc through Howard University. As a planetary scientist for the James Webb Space Telescope, she’s an expert on the atmospheres of the ice giants in our solar system — Uranus and Neptune — and how the Webb telescope will be able to learn more about them.
The James Webb Space Telescope – fun facts:
Webb is so big it has to fold origami-style to fit into its rocket and will unfold like a “Transformer” in space.
Webb is about 100 times more powerful than the Hubble Space Telescope and designed to see the infrared, a region Hubble can only peek at.
With unprecedented sensitivity, it will peer back in time over 13.5 billion years to see the first galaxies born after the Big Bang––a part of space we’ve never seen.
It will study galaxies near and far, young and old, to understand how they evolve.
Webb will explore distant worlds and study the atmospheres of planets orbiting other stars, known as exoplanets, searching for chemical fingerprints of possible habitability.
Follow, follow the Sun / And which way the wind blows / When this day is done 🎶 Today, April 8, 2024, the last total solar eclipse until 2045 crossed North America.
