If You’ve Ever Watched Water Running Down The Side Of The Street, You’ve Probably Noticed That It

After the rain of Hurricane Florence came the rainbow, or rainbows, in this case. Photographer John Entwistle captured this image of a rainbow with several additional supernumerary bows. The inner fringes seen here form when light passes through water droplets that are all close to the same size; given the spread seen here, the droplets are likely smaller than a millimeter in diameter. Supernumerary rainbows cannot be explained with a purely geometric theory of optics; instead, they require acknowledging the wave nature of light. (Image credit: J. Entwistle; via APOD; submitted by Kam-Yung Soh)

Gamma-ray Bursts: Black Hole Birth Announcements

Gamma-ray bursts are the brightest, most violent explosions in the universe, but they can be surprisingly tricky to detect. Our eyes can’t see them because they are tuned to just a limited portion of the types of light that exist, but thanks to technology, we can even see the highest-energy form of light in the cosmos — gamma rays.

So how did we discover gamma-ray bursts? 

Accidentally!

We didn’t actually develop gamma-ray detectors to peer at the universe — we were keeping an eye on our neighbors! During the Cold War, the United States and the former Soviet Union both signed the Nuclear Test Ban Treaty of 1963 that stated neither nation would test nuclear weapons in space. Just one week later, the US launched the first Vela satellite to ensure the treaty wasn’t being violated. What they saw instead were gamma-ray events happening out in the cosmos!

Things Going Bump in the Cosmos

Each of these gamma-ray events, dubbed “gamma-ray bursts” or GRBs, lasted such a short time that information was very difficult to gather. For decades their origins, locations and causes remained a cosmic mystery, but in recent years we’ve been able to figure out a lot about GRBs. They come in two flavors: short-duration (less than two seconds) and long-duration (two seconds or more). Short and long bursts seem to be caused by different cosmic events, but the end result is thought to be the birth of a black hole.

Short GRBs are created by binary neutron star mergers. Neutron stars are the superdense leftover cores of really massive stars that have gone supernova. When two of them crash together (long after they’ve gone supernova) the collision releases a spectacular amount of energy before producing a black hole. Astronomers suspect something similar may occur in a merger between a neutron star and an already-existing black hole.

Long GRBs account for most of the bursts we see and can be created when an extremely massive star goes supernova and launches jets of material at nearly the speed of light (though not every supernova will produce a GRB). They can last just a few seconds or several minutes, though some extremely long GRBs have been known to last for hours!

A Gamma-Ray Burst a Day Sends Waves of Light Our Way!

Our Fermi Gamma-ray Space Telescope detects a GRB nearly every day, but there are actually many more happening — we just can’t see them! In a GRB, the gamma rays are shot out in a narrow beam. We have to be lined up just right in order to detect them, because not all bursts are beamed toward us — when we see one it’s because we’re looking right down the barrel of the gamma-ray gun. Scientists estimate that there are at least 50 times more GRBs happening each day than we detect!

So what’s left after a GRB — just a solitary black hole? Since GRBs usually last only a matter of seconds, it’s very difficult to study them in-depth. Fortunately, each one leaves an afterglow that can last for hours or even years in extreme cases. Afterglows are created when the GRB jets run into material surrounding the star. Because that material slows the jets down, we see lower-energy light, like X-rays and radio waves, that can take a while to fade. Afterglows are so important in helping us understand more about GRBs that our Neil Gehrels Swift Observatory was specifically designed to study them!

Last fall, we had the opportunity to learn even more from a gamma-ray burst than usual! From 130 million light-years away, Fermi witnessed a pair of neutron stars collide, creating a spectacular short GRB. What made this burst extra special was the fact that ground-based gravitational wave detectors LIGO and Virgo caught the same event, linking light and gravitational waves to the same source for the first time ever!

For over 10 years now, Fermi has been exploring the gamma-ray universe. Thanks to Fermi, scientists are learning more about the fundamental physics of the cosmos, from dark matter to the nature of space-time and beyond. Discover more about how we’ll be celebrating Fermi’s achievements all year!

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com

Aurora Over Alaska (by HB Mertz)

5 Facts About Earth's Radiation Donuts 🍩

Did you know that our planet is surrounded by giant, donut-shaped clouds of radiation?

Here’s what you need to know.

1. The radiation belts are a side effect of Earth’s magnetic field

The Van Allen radiation belts exist because fast-moving charged particles get trapped inside Earth’s natural magnetic field, forming two concentric donut-shaped clouds of radiation. Other planets with global magnetic fields, like Jupiter, also have radiation belts.

2. The radiation belts were one of our first Space Age discoveries

Earth’s radiation belts were first identified in 1958 by Explorer 1, the first U.S. satellite. The inner belt, composed predominantly of protons, and the outer belt, mostly electrons, would come to be named the Van Allen Belts, after James Van Allen, the scientist who led the charge designing the instruments and studying the radiation data from Explorer 1.

3. The Van Allen Probes have spent six years exploring the radiation belts

In 2012, we launched the twin Van Allen Probes to study the radiation belts. Over the past six years, these spacecraft have orbited in and out of the belts, providing brand-new data about how the radiation belts shift and change in response to solar activity and other factors.

4. Surprise! Sometimes there are three radiation belts

Shortly after launch, the Van Allen Probes detected a previously-unknown third radiation belt, created by a bout of strong solar activity. All the extra energy directed towards Earth meant that some particles trapped in our planet’s magnetic field were swept out into the usually relatively empty region between the two Van Allen Belts, creating an additional radiation belt.

5. Swan song for the Van Allen Probes

Originally designed for a two-year mission, the Van Allen Probes have spent more than six years collecting data in the harsh radiation environment of the Van Allen Belts. In spring 2019, we’re changing their orbit to bring the perigee — the part of the orbit where the spacecraft are closest to Earth — about 190 miles lower. This ensures that the spacecraft will eventually burn up in Earth’s atmosphere, instead of orbiting forever and becoming space junk.

Because the Van Allen Probes have proven to be so hardy, they’ll continue collecting data throughout the final months of the mission until they run out of fuel. As they skim through the outer reaches of Earth’s atmosphere, scientists and engineers will also learn more about how atmospheric oxygen can degrade satellite measurements — information that can help build better satellites in the future.

Keep up with the latest on the mission on Twitter, Facebook or nasa.gov/vanallenprobes.

Saturn’s rings and our planet Earth and Moon in the same frame captured by nasa’s Cassini spacecraft 19 July. (source @nasa) *Out Pale Blue Dot*

Dust, stars, and cosmic rays swirling around Comet 67P/Churyumov–Gerasimenko, captured by the Rosetta probe. (Source)

How Big is Our Galaxy, the Milky Way?

When we talk about the enormity of the cosmos, it’s easy to toss out big numbers – but far harder to wrap our minds around just how large, how far and how numerous celestial bodies like exoplanets – planets beyond our solar system – really are.

So. How big is our Milky Way Galaxy?

We use light-time to measure the vast distances of space.

It’s the distance that light travels in a specific period of time. Also: LIGHT IS FAST, nothing travels faster than light.

How far can light travel in one second? 186,000 miles. It might look even faster in metric: 300,000 kilometers in one second. See? FAST.

How far can light travel in one minute? 11,160,000 miles. We’re moving now! Light could go around the Earth a bit more than 448 times in one minute.

Speaking of Earth, how long does it take light from the Sun to reach our planet? 8.3 minutes. (It takes 43.2 minutes for sunlight to reach Jupiter, about 484 million miles away.) Light is fast, but the distances are VAST.

In an hour, light can travel 671 million miles. We’re still light-years from the nearest exoplanet, by the way. Proxima Centauri b is 4.2 light-years away. So… how far is a light-year? 5.8 TRILLION MILES.

A trip at light speed to the very edge of our solar system – the farthest reaches of the Oort Cloud, a collection of dormant comets way, WAY out there – would take about 1.87 years.

Our galaxy contains 100 to 400 billion stars and is about 100,000 light-years across!

One of the most distant exoplanets known to us in the Milky Way is Kepler-443b. Traveling at light speed, it would take 3,000 years to get there. Or 28 billion years, going 60 mph. So, you know, far.

SPACE IS BIG.

Read more here: go.nasa.gov/2FTyhgH

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com.

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Blue Straggler Stars in Globular Cluster M53 

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“The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ (I’ve found it!), but ‘That’s funny…’”

— Isaac Asimov | Author - I, Robot | Professor - Biochemistry