Gravitational waves are disturbances in space-time, the very fabric of the universe, that travel at the speed of light. The waves are emitted by any mass that is changing speed or direction. The simplest example is a binary system, where a pair of stars or compact objects (like black holes) orbit their common center of mass.
We can think of gravitational effects as curvatures in space-time. Earth’s gravity is constant and produces a static curve in space-time. A gravitational wave is a curvature that moves through space-time much like a water wave moves across the surface of a lake. It is generated only when masses are speeding up, slowing down or changing direction.
Did you know Earth also gives off gravitational waves? Earth orbits the sun, which means its direction is always changing, so it does generate gravitational waves, although extremely weak and faint.
What do we learn from these waves?
Observing gravitational waves would be a huge step forward in our understanding of the evolution of the universe, and how large-scale structures, like galaxies and galaxy clusters, are formed.
Gravitational waves can travel across the universe without being impeded by intervening dust and gas. These waves could also provide information about massive objects, such as black holes, that do not themselves emit light and would be undetectable with traditional telescopes.
Just as we need both ground-based and space-based optical telescopes, we need both kinds of gravitational wave observatories to study different wavelengths. Each type complements the other.
Ground-based: For optical telescopes, Earth’s atmosphere prevents some wavelengths from reaching the ground and distorts the light that does.
Space-based: Telescopes in space have a clear, steady view. That said, telescopes on the ground can be much larger than anything ever launched into space, so they can capture more light from faint objects.
How does this relate to Einstein’s theory of relativity?
The direct detection of gravitational waves is the last major prediction of Einstein’s theory to be proven. Direct detection of these waves will allow scientists to test specific predictions of the theory under conditions that have not been observed to date, such as in very strong gravitational fields.
In everyday language, “theory” means something different than it does to scientists. For scientists, the word refers to a system of ideas that explains observations and experimental results through independent general principles. Isaac Newton’s theory of gravity has limitations we can measure by, say, long-term observations of the motion of the planet Mercury. Einstein’s relativity theory explains these and other measurements. We recognize that Newton’s theory is incomplete when we make sufficiently sensitive measurements. This is likely also true for relativity, and gravitational waves may help us understand where it becomes incomplete.
Gravity has been making waves - literally. Earlier this month, the Nobel Prize in Physics was awarded for the first direct detection of gravitational waves two years ago. But astronomers just announced another huge advance in the field of gravitational waves - for the first time, we’ve observed light and gravitational waves from the same source.
There was a pair of orbiting neutron stars in a galaxy (called NGC 4993). Neutron stars are the crushed leftover cores of massive stars (stars more than 8 times the mass of our sun) that long ago exploded as supernovas. There are many such pairs of binaries in this galaxy, and in all the galaxies we can see, but something special was about to happen to this particular pair.
Each time these neutron stars orbited, they would lose a teeny bit of gravitational energy to gravitational waves. Gravitational waves are disturbances in space-time - the very fabric of the universe - that travel at the speed of light. The waves are emitted by any mass that is changing speed or direction, like this pair of orbiting neutron stars. However, the gravitational waves are very faint unless the neutron stars are very close and orbiting around each other very fast.
As luck would have it, the teeny energy loss caused the two neutron stars to get a teeny bit closer to each other and orbit a teeny bit faster. After hundreds of millions of years, all those teeny bits added up, and the neutron stars were *very* close. So close that … BOOM! … they collided. And we witnessed it on Earth on August 17, 2017.
Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet
A couple of very cool things happened in that collision - and we expect they happen in all such neutron star collisions. Just before the neutron stars collided, the gravitational waves were strong enough and at just the right frequency that the National Science Foundation (NSF)’s Laser Interferometer Gravitational-Wave Observatory (LIGO) and European Gravitational Observatory’s Virgo could detect them. Just after the collision, those waves quickly faded out because there are no longer two things orbiting around each other!
LIGO is a ground-based detector waiting for gravitational waves to pass through its facilities on Earth. When it is active, it can detect them from almost anywhere in space.
The other thing that happened was what we call a gamma-ray burst. When they get very close, the neutron stars break apart and create a spectacular, but short, explosion. For a couple of seconds, our Fermi Gamma-ray Telescope saw gamma-rays from that explosion. Fermi’s Gamma-ray Burst Monitor is one of our eyes on the sky, looking out for such bursts of gamma-rays that scientists want to catch as soon as they’re happening.
And those gamma-rays came just 1.7 seconds after the gravitational wave signal. The galaxy this occurred in is 130 million light-years away, so the light and gravitational waves were traveling for 130 million years before we detected them.
After that initial burst of gamma-rays, the debris from the explosion continued to glow, fading as it expanded outward. Our Swift, Hubble, Chandra and Spitzer telescopes, along with a number of ground-based observers, were poised to look at this afterglow from the explosion in ultraviolet, optical, X-ray and infrared light. Such coordination between satellites is something that we’ve been doing with our international partners for decades, so we catch events like this one as quickly as possible and in as many wavelengths as possible.
Astronomers have thought that neutron star mergers were the cause of one type of gamma-ray burst - a short gamma-ray burst, like the one they observed on August 17. It wasn’t until we could combine the data from our satellites with the information from LIGO/Virgo that we could confirm this directly.
This event begins a new chapter in astronomy. For centuries, light was the only way we could learn about our universe. Now, we’ve opened up a whole new window into the study of neutron stars and black holes. This means we can see things we could not detect before.
The first LIGO detection was of a pair of merging black holes. Mergers like that may be happening as often as once a month across the universe, but they do not produce much light because there’s little to nothing left around the black hole to emit light. In that case, gravitational waves were the only way to detect the merger.
Image Credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)
The neutron star merger, though, has plenty of material to emit light. By combining different kinds of light with gravitational waves, we are learning how matter behaves in the most extreme environments. We are learning more about how the gravitational wave information fits with what we already know from light - and in the process we’re solving some long-standing mysteries!
But before we get to dark energy, let’s first talk a bit about the expanding cosmos. It started with the big bang — when the universe started expanding from a hot, dense state about 13.8 billion years ago. Our universe has been getting bigger and bigger ever since. Nearly every galaxy we look at is zipping away from us, caught up in that expansion!
The expansion, though, is even weirder than you might imagine. Things aren’t actually moving away from each other. Instead, the space between them is getting larger.
Imagine that you and a friend were standing next to each other. Just standing there, but the floor between you was growing. You two aren’t technically moving, but you see each other moving away. That’s what’s happening with the galaxies (and everything else) in our cosmos … in ALL directions!
Astronomers expected the expansion to slow down over time. Why? In a word: gravity. Anything that has mass or energy has gravity, and gravity tries to pull stuff together. Plus, it works over the longest distances. Even you, reading this, exert a gravitational tug on the farthest galaxy in the universe! It’s a tiny tug, but a tug nonetheless.
As the space between galaxies grows, gravity is trying to tug the galaxies back together — which should slow down the expansion. So, if we measure the distance of faraway galaxies over time, we should be able to detect if the universe’s growth rate slows down.
⬆️ This graphic illustrates the history of our expanding universe. We do see some slowing down of the expansion (the uphill part of the graph, where the roller coaster is slowing down). However, at some point, dark energy overtakes gravity and the expansion speeds up (the downhill on the graph). It’s like our universe is on a giant roller coaster ride, but we’re not sure how steep the hill is!
We don’t know exactly what dark energy is, and we’ve never detected it directly. But we do know there is a lot of it. A lot. If you summed up all the “stuff” in the universe — normal matter (the stuff we can touch or observe directly), dark matter, and dark energy — dark energy would make up more than two-thirds of what is out there.
That’s a lot of our universe to have escaped detection!
Researchers have come up with a few dark energy possibilities. Einstein discarded an idea from his theory of general relativity about an intrinsic property of space itself. It could be that this bit of theory got dark energy right after all. Perhaps instead there is some strange kind of energy-fluid that fills space. It could even be that we need to tweak Einstein’s theory of gravity to work at the largest scales.
Our Wide Field Infrared Survey Telescope (WFIRST) — planned to launch in the mid-2020s — will be helping with the task of unraveling the mystery of dark energy. WFIRST will map the structure and distribution of matter throughout the cosmos and across cosmic time. It will also map the universe’s expansion and study galaxies from when the universe was a wee 2-billion-year-old up to today. Using these new data, researchers will learn more than we’ve ever known about dark energy. Perhaps even cracking open the case!
You can find out more about the history of dark energy and how a number of different pieces of observational evidence led to its discovery in our Cosmic Times series. And keep an eye on WFIRST to see how this mystery unfolds.
One
hundred years ago, on May 29, 1919, astronomers observed a total solar eclipse in
an ambitious effort to test Albert
Einstein’s general theory of relativity by seeing it in action. Essentially, Einstein
thought space and time were intertwined in an infinite “fabric,” like an
outstretched blanket. A massive object such as the Sun bends the spacetime blanket
with its gravity, such that light no longer travels in a straight line as it passes
by the Sun.
This
means the apparent positions of background stars seen close to the Sun in the
sky – including during a solar eclipse – should seem slightly shifted in the
absence of the Sun, because the Sun’s gravity bends light. But until the
eclipse experiment, no one was able to test Einstein’s theory of general
relativity, as no one could see stars near the Sun in the daytime otherwise.
The
world celebrated the results of this eclipse experiment— a victory for
Einstein, and the dawning of a new era of our understanding of the universe.
General
relativity has many important consequences for what we see in the cosmos and
how we make discoveries in deep space today. The same is true for Einstein’s slightly
older theory, special relativity, with its widely celebrated equation E=mc². Here
are 10 things that result from Einstein’s theories of relativity:
1. Universal Speed Limit
Einstein’s
famous equation
E=mc²
contains “c,” the speed of light in a vacuum. Although
light comes in many flavors – from the rainbow of colors humans can see to the
radio waves that transmit spacecraft data – Einstein said all light must obey
the speed limit of 186,000 miles (300,000 kilometers) per second. So, even if
two particles of light carry very different amounts of energy, they will travel
at the same speed.
This
has been shown experimentally in space. In 2009, our Fermi Gamma-ray Space Telescope detected two photons at virtually the same moment, with one carrying a million
times more energy than the other. They both came from a high-energy region near
the collision of two neutron stars about 7 billion years ago. A neutron star is
the highly dense remnant of a star that has exploded. While other theories
posited that space-time itself has a “foamy” texture that might slow down more energetic
particles, Fermi’s observations found in favor of Einstein.
2. Strong Lensing
Just
like the Sun bends the light from distant stars that pass close to it, a
massive object like a galaxy distorts the light from another object that is
much farther away. In some cases, this phenomenon can actually help us unveil
new galaxies. We say that the closer object acts like a “lens,” acting like a
telescope that reveals the more distant object. Entire clusters of galaxies can
be lensed and act as lenses, too.
When
the lensing object appears close enough to the more distant object in the sky,
we actually see multiple images of that faraway object. In 1979, scientists
first observed a double image of a quasar, a very bright object at the center
of a galaxy that involves a supermassive black hole feeding off a disk of
inflowing gas. These apparent copies of the distant object change in brightness
if the original object is changing, but not all at once, because of how space
itself is bent by the foreground object’s gravity.
Sometimes,
when a distant celestial object is precisely aligned with another object, we
see light bent into an “Einstein ring” or arc. In this image from our Hubble Space
Telescope,
the sweeping arc of light represents a distant galaxy that has been lensed,
forming a “smiley face” with other galaxies.
3. Weak Lensing
When
a massive object acts as a lens for a farther object, but the objects are not specially
aligned with respect to our view, only one image of the distant object is
projected. This happens much more often. The closer object’s gravity makes the
background object look larger and more stretched than it really is. This is
called “weak lensing.”
Weak
lensing is very important for studying some of the biggest mysteries of the
universe: dark matter and dark energy. Dark matter is an invisible material
that only interacts with regular matter through gravity, and holds together
entire galaxies and groups of galaxies like a cosmic glue. Dark energy behaves like
the opposite of gravity, making objects recede from each other. Three upcoming
observatories – Our Wide Field Infrared
Survey Telescope,
WFIRST, mission, the European-led Euclid space mission with NASA participation,
and the ground-based Large Synoptic Survey Telescope
— will be key players in this effort. By surveying distortions of weakly lensed
galaxies across the universe, scientists can characterize the effects of these persistently
puzzling phenomena.
Gravitational
lensing in general will also enable NASA’s James Webb Space telescope to look
for some of the very first stars and galaxies of the universe.
4. Microlensing
So
far, we’ve been talking about giant objects acting like magnifying lenses for
other giant objects. But stars can also “lens” other stars, including stars
that have planets around them. When light from a background star gets “lensed”
by a closer star in the foreground, there is an increase in the background
star’s brightness. If that foreground star also has a planet orbiting it, then
telescopes can detect an extra bump in the background star’s light, caused by
the orbiting planet. This technique for finding exoplanets, which are planets
around stars other than our own, is called “microlensing.”
Our Spitzer Space Telescope, in collaboration with ground-based
observatories, found an “iceball” planet through microlensing. While
microlensing has so far found less than 100 confirmed planets, WFIRST could find more than 1,000 new
exoplanets using this technique.
5. Black Holes
The
very existence of black holes, extremely dense objects from which no light can escape, is a prediction
of general relativity. They represent the most extreme distortions of the
fabric of space-time, and are especially famous for how their immense gravity affects
light in weird ways that only Einstein’s theory could explain.
In
2019 the Event Horizon Telescope international collaboration, supported by the
National Science Foundation and other partners, unveiled the first image of a black hole’s event
horizon,
the border that defines a black hole’s “point of no return” for nearby
material. NASA’s Chandra
X-ray Observatory, Nuclear
Spectroscopic Telescope Array (NuSTAR),
Neil Gehrels Swift Observatory, and Fermi Gamma-ray Space Telescope all looked
at the same black hole in a coordinated effort, and researchers are still
analyzing the results.
6. Relativistic Jets
This
Spitzer image shows the galaxy Messier 87 (M87) in infrared light, which has a
supermassive black hole at its center. Around the black hole is a disk of
extremely hot gas, as well as two jets of material shooting out in opposite
directions. One of the jets, visible on the right of the image, is pointing
almost exactly toward Earth. Its enhanced brightness is due to the emission of light
from particles traveling toward the observer at near the speed of light, an
effect called “relativistic beaming.” By contrast, the other jet is invisible
at all wavelengths because it is traveling away from the observer near the
speed of light. The details of how such jets work are still mysterious, and
scientists will continue studying black holes for more clues.
7. A Gravitational Vortex
Speaking
of black holes, their gravity is so intense that they make infalling material
“wobble” around them. Like a spoon stirring honey, where honey is the space
around a black hole, the black hole’s distortion of space has a wobbling effect
on material orbiting the black hole. Until recently, this was only theoretical.
But in 2016, an international team of scientists using European Space Agency’s XMM-Newton and our Nuclear Spectroscopic Telescope Array (NUSTAR) announced they had observed the signature of wobbling
matter for the first time. Scientists will continue studying these odd effects
of black holes to further probe Einstein’s ideas firsthand.
Incidentally,
this wobbling of material around a black hole is similar to how Einstein
explained Mercury’s odd orbit. As the closest planet to the Sun, Mercury feels
the most gravitational tug from the Sun, and so its orbit’s orientation is
slowly rotating around the Sun, creating a wobble.
8. Gravitational Waves
Ripples
through space-time called gravitational waves were hypothesized by Einstein
about 100 years ago, but not actually observed until recently. In 2016, an
international collaboration of astronomers working with the Laser Interferometer
Gravitational-Wave Observatory (LIGO)
detectors announced a landmark discovery: This enormous experiment detected the
subtle signal of gravitational waves that had been traveling for 1.3 billion
years after two black holes merged in a cataclysmic event. This opened a brand
new door in an area of science called multi-messenger astronomy, in which both
gravitational waves and light can be studied.
For example,
our telescopes collaborated to measure light from two neutron stars
merging after LIGO detected gravitational wave signals from the event, as
announced in 2017. Given that gravitational waves from this event were detected
mere 1.7 seconds before gamma rays from the merger, after both traveled 140
million light-years, scientists concluded Einstein was right about something
else: gravitational waves and light waves travel at the same speed.
9. The Sun Delaying Radio Signals
Planetary
exploration spacecraft have also shown Einstein to be right about general
relativity. Because spacecraft communicate with Earth using light, in the form
of radio waves, they present great opportunities to see whether the gravity of
a massive object like the Sun changes light’s path.
In
1970, our Jet Propulsion Laboratory announced that Mariner VI and VII,
which completed flybys of Mars in 1969, had conducted experiments using radio
signals — and also agreed with Einstein. Using NASA’s
Deep Space Network (DSN), the two Mariners took several hundred radio measurements for
this purpose. Researchers measured the time it took for radio signals to travel
from the DSN dish in Goldstone, California, to the spacecraft and back. As
Einstein would have predicted, there was a delay in the total roundtrip time
because of the Sun’s gravity. For Mariner VI, the maximum delay was 204
microseconds, which, while far less than a single second, aligned almost
exactly with what Einstein’s theory would anticipate.
In
1979, the Viking landers performed an even more accurate experiment along these
lines. Then, in 2003 a group of scientists used NASA’s Cassini Spacecraft to repeat these kinds of
radio science experiments with 50 times greater precision than Viking. It’s
clear that Einstein’s theory has held up!
10. Proof from Orbiting
Earth
In
2004, we launched a spacecraft called Gravity
Probe B
specifically designed to watch Einstein’s theory play out in the orbit of
Earth. The theory goes that Earth, a rotating body, should be pulling the
fabric of space-time around it as it spins, in addition to distorting light with
its gravity.
The
spacecraft had four gyroscopes and pointed at the star IM Pegasi while orbiting
Earth over the poles. In this experiment, if Einstein had been wrong, these
gyroscopes would have always pointed in the same direction. But in 2011,
scientists announced they had observed tiny changes in the gyroscopes’
directions as a consequence of Earth, because of its gravity, dragging space-time
around it.
BONUS: Your GPS! Speaking of time delays, the
GPS (global positioning system) on your phone or in your car relies on Einstein’s
theories for accuracy. In order to know where you are, you need a receiver –
like your phone, a ground station and a network of satellites orbiting Earth to
send and receive signals. But according to general relativity, because of
Earth’s gravity curving spacetime, satellites experience time moving slightly
faster than on Earth. At the same time, special relativity would say time moves
slower for objects that move much faster than others.
When
scientists worked out the net effect of these forces, they found that the
satellites’ clocks would always be a tiny bit ahead of clocks on Earth. While
the difference per day is a matter of millionths of a second, that change
really adds up. If GPS didn’t have relativity built into its technology, your
phone would guide you miles out of your way!
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One hundred years ago a total solar eclipse turned an obscure scientist into a household name. You might have heard of him — his name is Albert Einstein. But how did a solar eclipse propel him to fame?
A decade before he finished general relativity, Einstein published his special theory of relativity, which demonstrates how space and time are interwoven as a single structure he dubbed “space-time.” General relativity extended the foundation of special relativity to include gravity. Einstein realized that gravitational fields can be understood as bends and curves in space-time that affect the motions of objects including stars, planets — and even light.
For everyday situations the centuries-old description of gravity by Isaac Newton does just fine. However, general relativity must be accounted for when we study places with strong gravity, like black holes or neutron stars, or when we need very precise measurements, like pinpointing a position on Earth to within a few feet. That makes it hard to test!
A prediction of general relativity is that light passing by an object feels a slight “tug”, causing the light’s path to bend slightly. The more mass the object has, the more the light will be deflected. This sets up one of the tests that Einstein suggested — measuring how starlight bends around the Sun, the strongest source of gravity in our neighborhood. Starlight that passes near the edge of the Sun on its way to Earth is deflected, altering by a small amount where those stars appear to be. How much? By about the width of a dime if you saw it at a mile and a quarter away! But how can you observe faint stars near the brilliant Sun? During a total solar eclipse!
That’s where the May 29, 1919, total solar eclipse comes in. Two teams were dispatched to locations in the path of totality — the places on Earth where the Moon will appear to completely cover the face of the Sun during an eclipse. One team went to South America and another to Africa.
On eclipse day, the sky vexed both teams, with rain in Africa and clouds in South America. The teams had only mere minutes of totality during which to take their photographs, or they would lose the opportunity until the next total solar eclipse in 1921! However, the weather cleared at both sites long enough for the teams to take images of the stars during totality.
The teams took two sets of photographs of the same patch of sky – one set during the eclipse and another set a few months before or after, when the Sun was out of the way. By comparing these two sets of photographs, researchers could see if the apparent star positions changed as predicted by Einstein. This is shown with the effect exaggerated in the image above.
The solar eclipse wasn’t the first test of general relativity. For more than two centuries, astronomers had known that Mercury’s orbit was a little off. Its perihelion — the point during its orbit when it is closest to the Sun — was changing faster than Newton’s laws predicted. General relativity easily explains it, though, because Mercury is so close to the Sun that its orbit is affected by the Sun’s dent in space-time, causing the discrepancy.
You can also read more about how our understanding of the universe has changed during the past 100 years, from Einstein’s formulation of gravity through the discovery of dark energy in our Cosmic Times newspaper series.
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Our Sun has an entourage of planets, moons, and smaller objects to keep it company as it traverses the galaxy. But it’s still lonely compared to many of the other stars out there, which often come in pairs. These cosmic couples, called binary stars, are very important in astronomy because they can easily reveal things that are much harder to learn from stars that are on their own. And some of them could even host habitable planets!
The birth of a stellar duo
New stars emerge from swirling clouds of gas and dust that are peppered throughout the galaxy. Scientists still aren’t sure about all the details, but turbulence deep within these clouds may give rise to knots that are denser than their surroundings. The knots have stronger gravity, so they can pull in more material and the cloud may begin to collapse.
The material at the center heats up. Known as a protostar, it is this hot core that will one day become a star. Sometimes these spinning clouds of collapsing gas and dust may break up into two, three, or even more blobs that eventually become stars. That would explain why the majority of the stars in the Milky Way are born with at least one sibling.
Seeing stars
We can’t always tell if we’re looking at binary stars using just our eyes. They’re often so close together in the sky that we see them as a single star. For example, Sirius, the brightest star we can see at night, is actually a binary system (see if you can spot both stars in the photo above). But no one knew that until the 1800s.
Precise observations showed that Sirius was swaying back and forth like it was at a middle school dance. In 1862, astronomer Alvan Graham Clark used a telescope to see that Sirius is actually two stars that orbit each other.
But even through our most powerful telescopes, some binary systems still masquerade as a single star. Fortunately there are a couple of tricks we can use to spot these pairs too.
Since binary stars orbit each other, there’s a chance that we’ll see some stars moving toward and away from us as they go around each other. We just need to have an edge-on view of their orbits. Astronomers can detect this movement because it changes the color of the star’s light – a phenomenon known as the Doppler effect.
Stars we can find this way are called spectroscopic binaries because we have to look at their spectra, which are basically charts or graphs that show the intensity of light being emitted over a range of energies. We can spot these star pairs because light travels in waves. When a star moves toward us, the waves of its light arrive closer together, which makes its light bluer. When a star moves away, the waves are lengthened, reddening its light.
Sometimes we can see binary stars when one of the stars moves in front of the other. Astronomers find these systems, called eclipsing binaries, by measuring the amount of light coming from stars over time. We receive less light than usual when the stars pass in front of each other, because the one in front will block some of the farther star’s light.
Sibling rivalry
Twin stars don’t always get along with each other – their relationship may be explosive! Type Ia supernovae happen in some binary systems in which a white dwarf – the small, hot core left over when a Sun-like star runs out of fuel and ejects its outer layers – is stealing material away from its companion star. This results in a runaway reaction that ultimately detonates the thieving star. The same type of explosion may also happen when two white dwarfs spiral toward each other and collide. Yikes!
Scientists know how to determine how bright these explosions should truly be at their peak, making Type Ia supernovae so-called standard candles. That means astronomers can determine how far away they are by seeing how bright they look from Earth. The farther they are, the dimmer they appear. Astronomers can also look at the wavelengths of light coming from the supernovae to find out how fast the dying stars are moving away from us.
Astronomers like finding binary systems because it’s a lot easier to learn more about stars that are in pairs than ones that are on their own. That’s because the stars affect each other in ways we can measure. For example, by paying attention to how the stars orbit each other, we can determine how massive they are. Since heavier stars burn hotter and use up their fuel more quickly than lighter ones, knowing a star’s mass reveals other interesting things too.
By studying how the light changes in eclipsing binaries when the stars cross in front of each other, we can learn even more! We can figure out their sizes, masses, how fast they’re each spinning, how hot they are, and even how far away they are. All of that helps us understand more about the universe.
Tatooine worlds
Thanks to observatories such as our Kepler Space Telescope, we know that worlds like Luke Skywalker’s home planet Tatooine in “Star Wars” exist in real life. And if a planet orbits at the right distance from the two stars, it could even be habitable (and stay that way for a long time).
In 2019, our Transiting Exoplanet Survey Satellite (TESS) found a planet, known as TOI-1338 b, orbiting a pair of stars. These worlds are tricker to find than planets with only one host star, but TESS is expected to find several more!
Gravity rules everything on Earth, from how our bodies develop to what our research can reveal, but what happens when we go 250 miles up to the International Space Station?
Get ready to go behind the scenes of what it takes to get science to space, and meet the people who make it happen.
Introducing Season 4 of NASA Explorers: Microgravity. Floating isn’t just fun. Microgravity could open the door to discovery.
You’ve seen things floating in space, but why does that happen and how does it affect science being conducted aboard the International Space Station?
Microgravity makes the International Space Station the perfect place to perform research that is changing the lives of people on Earth, and preparing us to go deeper into space. This season on our series NASA Explorers, we are following science into low-Earth orbit and seeing what it takes to do research aboard the space station.
One hundred years ago this month, Albert Einstein published his theory of general relativity (GR), one of the most important scientific achievements in the last century.
A key result of Einstein’s theory is that matter warps space-time, and thus a massive object can cause an observable bending of light from a background object. The first success of the theory was the observation, during a solar eclipse, that light from a distant background star was deflected by the predicted amount as it passed near the sun.
When Einstein developed the general theory of relativity, he was trying to improve our understanding of how the universe works. At the time, Newtonian gravity was more than sufficient for any practical gravity calculations. However, as often happens in physics, general relativity has applications that would not have been foreseen by Einstein or his contemporaries.
How many of us have used a smartphone to get directions? Or to tag our location on social media? Or to find a recommendation for a nearby restaurant? These activities depend on GPS. GPS uses radio signals from a network of satellites orbiting Earth at an altitude of 20,000 km to pinpoint the location of a GPS receiver. The accuracy of GPS positioning depends on precision in time measurements of billionths of a second. To achieve such timing precision, however, relativity must be taken into account.
Our Gravity Probe B (GP-B) mission has confirmed two key predictions derived from Albert Einstein’s general theory of relativity, which the spacecraft was designed to test. The experiment, launched in 2004, and measured the warping of space and time around a gravitational body, and frame-dragging, the amount a spinning object pulls space and time with it as it rotates.
Scientists continue to look for cracks in the theory, testing general relativity predictions using laboratory experiments and astronomical observations. For the past century, Einstein’s theory of gravity has passed every hurdle.
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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LaRue Burbank, mathematician and computer, is just one of the many women who were instrumental to NASA missions.
4 Little Known Women Who Made Huge Contributions to NASA
Women have always played a significant role at NASA and its predecessor NACA, although for much of the agency’s history, they received neither the praise nor recognition that their contributions deserved. To celebrate Women’s History Month – and properly highlight some of the little-known women-led accomplishments of NASA’s early history – our archivists gathered the stories of four women whose work was critical to NASA’s success and paved the way for future generations.