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.
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?
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.
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.
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.