Gamma-ray Bursts: Nature’s Brightest Flash Bulbs

Discovered in the 1960s, when the United States launched satellites into orbit to verify the Atmospheric Test Ban Treaty, gamma-ray bursts have continued to amaze and astound scientists for over 40 years. These titanic events, which emit more energy in a single blast than is emitted from our Sun in its entire lifetime, appear briefly and then are never seen again from the same location in the cosmos. Gamma-ray bursts (or GRBs) are the brightest astrophysical light sources observed today.  Detectors on satellites orbiting the Earth detect an average of one GRB each day from somewhere in the Universe.

M82 lies 12 million light-years away in the constellation Ursa Major. Fermi’s LAT and the ground-based VERITAS observatory have detected diffuse gamma rays from the galaxy’s core, which produces stars at a rate ten times faster than our entire galaxy. Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA).

M82 lies 12 million light-years away in the constellation Ursa Major. Fermi’s LAT and the ground-based VERITAS observatory have detected diffuse gamma rays from the galaxy’s core, which produces stars at a rate ten times faster than our entire galaxy. Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA).

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How Do We Know What We Don’t Know About Asteroids?

What does guessing the number of jelly beans in a jar have to do with political polls and counting asteroids?  They all have something in common: all three use statistical samples to predict a result. In other words, without having to ask every single person in the country how they’ll vote, it’s possible to pick a group of people who we think are likely to be a good representation of everyone and just ask them how they’re going to vote. From this representative sample, we can predict what everyone else will do.

Similarly, we don’t have to count every single jelly bean in the jar to get a good estimate of how many there are. Instead, we can figure out about how big each bean is, and roughly how big the jar is, and from there, we can make a pretty solid guess about how many beans the jar holds.

When it comes to asteroids, those bits of rock, ice, and dust zooming around in our solar system, one of the first questions a lot of people ask is how many are there, and how do we know that? We certainly haven’t found all the asteroids yet, so how can we be sure how many there really are, and how many more are left to discover?

The Wide-field Infrared Survey Explorer (WISE) mission captured this infrared view of an Earth-orbiting satellite (green streak, lower right), the Main Belt Asteroid Regina (which appears as a string of orange dots, upper right), and the Triangulum Galaxy (center left), one of the closest galaxies to our own Milky Way. In this heat-sensitive infrared image, the shortest wavelengths are color-coded blue, and the longest are shown as red. Regina was detected by the WISE's mission asteroid-finding pipeline, known as NEOWISE. From its infrared signature, we can measure its size and the reflectivity of its surface. Regina is 47 km across, and its surface is as dark as black ink. It appears red in this image because it is much cooler than the stars, which are thousands of degrees. The string of red dots represents the multiple exposures of it that were collected by the WISE spacecraft. The satellite appears as a streak because it is much closer than the asteroid, so it appears to move much faster. Although the galaxy is moving incredibly fast, it is so far away that it appears stationary. Its blue stars are very hot, thousands of degrees, and the red regions highlight the cool, dusty locations where new stars are forming. Credit: NASA.

The Wide-field Infrared Survey Explorer (WISE) mission captured this infrared view of an Earth-orbiting satellite (green streak, lower right), the Main Belt Asteroid Regina (which appears as a string of orange dots, upper right), and the Triangulum Galaxy (center left), one of the closest galaxies to our own Milky Way. In this heat-sensitive infrared image, the shortest wavelengths are color-coded blue, and the longest are shown as red. Regina was detected by the WISE’s mission asteroid-finding pipeline, known as NEOWISE. From its infrared signature, we can measure its size and the reflectivity of its surface. Regina is 47 km across, and its surface is as dark as black ink. It appears red in this image because it is much cooler than the stars, which are thousands of degrees. The string of red dots represents the multiple exposures of it that were collected by the WISE spacecraft. The satellite appears as a streak because it is much closer than the asteroid, so it appears to move much faster. Although the galaxy is moving incredibly fast, it is so far away that it appears stationary. Its blue stars are very hot, thousands of degrees, and the red regions highlight the cool, dusty locations where new stars are forming. Credit: NASA.

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The sunlight that we cannot see

Imagine the Sun’s surface as an utterly black sphere. Imagine a cloudscape above this that is comprised of colorful fans of glowing wisps of translucent fog, all vastly larger than the Earth, which are continually swaying and pulsing, occasionally being torn apart by lightning storms of literally astronomical proportions.

Difficult? Not with some of the remarkable telescopes onboard NASA’s Solar Dynamics Observatory (SDO). They see that dynamic cloudscape, the Sun’s outer atmosphere, all the time, every day of the year, taking a picture almost every second over the past five years. These telescopes look at the Sun’s extreme ultraviolet (EUV) glow. That glow comes only from parts of the Sun’s atmosphere where the temperature exceeds a million degrees. Not from the solar surface that is  ‘merely’ a few thousand degrees, and that consequently is simply black in SDO’s EUV images.

Images taken by NASA’s Solar Dynamics Observatory on October 24, 2014. The image on the left shows the Sun’s hot atmosphere in extreme ultraviolet (EUV) light, with colors measuring temperature: blue is about 1.1 million degrees Celsius, green about 1.6 million, and red 2.2 million. The image on the right is taken in visible light at the same time, showing how we would see the Sun if viewed with a safe telescope. The sunspots seen on that day were the largest in over 25 years; the Earth would easily fit into the dark core of the largest spot. Credit NASA

Images taken by NASA’s Solar Dynamics Observatory on October 24, 2014. The image on the left shows the Sun’s hot atmosphere in extreme ultraviolet (EUV) light, with colors measuring temperature: blue is about 1.1 million degrees Celsius, green about 1.6 million, and red 2.2 million. The image on the right is taken in visible light at the same time, showing how we would see the Sun if viewed with a safe telescope. The sunspots seen on that day were the largest in over 25 years; the Earth would easily fit into the dark core of the largest spot. Credit NASA

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The Universe in X-ray Light

When I stop and think about it, it never ceases to amaze me that radio waves, infrared light, which we experience as heat, x-rays and gamma-rays are all the same fundamental physical phenomenon – light, or electromagnetic radiation.   The thing that distinguishes these different kinds of light is the wavelength.  Think of waves on the ocean, and taking out a ruler and measuring the distance between crests – that is the wavelength, only for light we are measuring the distance between ripples in electric and magnetic fields. For radio waves the wavelength is the size of a building, for X-rays it is the size of an atom. Astronomers use light of all wavelengths to understand the nature of the universe.

X-ray astronomers use telescopes that collect the same kind of light that your dentist and doctor use to see through your skin to study some of the hottest, densest and most extreme environments in the universe. X-rays are emitted from regions where material is heated to 10 – 100 million degrees Celsius, from places where particles are accelerated very close to the speed of light, and from intense cosmic explosions that are the death cries of massive stars. Regions that glow in X-rays range from the largest objects in the Universe that are held together by gravity, called galaxy clusters, to the most compact objects, like black holes and neutron stars.

X-rays are electromagnetic radiation just like radio waves, optical and infrared light.    X-rays have a wavelength the size of an atom, and must be observed from above Earth’s atmosphere by telescopes such as Chandra, XMM-Newton and NuSTAR. Credit: NASA.

X-rays are electromagnetic radiation just like radio waves, optical and infrared light. X-rays have a wavelength the size of an atom, and must be observed from above Earth’s atmosphere by telescopes such as Chandra, XMM-Newton and NuSTAR. Credit: NASA.

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Using Light to Probe the Heights of the Atmosphere and the Depths of the Ocean

Whether walking down a city street near a crowded nightclub opening or pulling up to the parking lot at the local county fair, it’s probably a safe bet that you’ve seen those bright, white searchlights flitting across the dark nighttime sky – the outline of the light beam clearly visible as it reaches up to touch the bottoms of the clouds overhead.  As a signal that can be seen far and wide, searchlights have a way of drawing you in to the main event. Hollywood producers certainly know this to be true.  For example, the next time you sit down with a bowl of popcorn to watch a 20th Century Fox movie, note the searchlights scanning the hazy skies in the opening credits.  Part of the reason searchlights are so captivating is that when we shine them up into the heavens, the light doesn’t just travel up to be lost into space – much of it is reflected by particles, clouds, and gases in the Earth’s atmosphere back down to the ground where we can see it.

Two lidar beams look up into the sky from the roof of the optical remote sensing laboratory at Montana State University in Bozeman, Montana, USA. The visible green laser beam is measuring the atmospheric profile of aerosols and clouds, while the invisible infrared laser beam is measuring water vapor. The lidars are in a laboratory on the top floor of the engineering building and transmit to the atmosphere through a roof port hatch. Credit: NASA/A. Nehrir.

Two lidar beams look up into the sky from the roof of the optical remote sensing laboratory at Montana State University in Bozeman, Montana, USA. The visible green laser beam is measuring the atmospheric profile of aerosols and clouds, while the invisible infrared laser beam is measuring water vapor. The lidars are in a laboratory on the top floor of the engineering building and transmit to the atmosphere through a roof port hatch. Credit: NASA/A. Nehrir.

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