The Denver Astronomical Society held its annual Holiday Party recently. A fine festival of maple-brined chicken and good company at the swanky Hilton. But the speaker really stood out – Dr. John Bally, a Colorado University professor of astrophysics. He was there to give us a talk on the current state of astronomy. I left being blown away.
We all read – or skip – all those astronomy stories that pop up constantly in our internet feeds. This satellite found this, that telescope saw that, and the resulting inferences from all of that data. It’s a constant stream of minutia, interesting though it all may be. Lost in all of that small-picture noise is the BIG PICTURE.
Dr. Bally pointed out what remarkable times we live in now, in terms of astronomy. Now, of course, this is a truism – we already know this, what with Hubble and many other telescopes, both ground-based and circling the earth, providing us with startling images and discoveries on practically a daily basis. But there are things you don’t know, or just don’t realize you know, until someone else points it out to you.
Up until about 50 years ago, all of the astronomical information we had about the universe was collected solely by ground-based telescopes, operating almost exclusively in just in the visual spectrum. Red, orange, yellow, green, blue, indigo, and violet light. That’s it. And visual is only one extremely narrow slice of the huge EM spectrum. Have a look:
Note the wavelength scale near the top; the visible spectrum runs from 400 to 700 nanometers. A nanometer is one-millionth of a millimeter, so as the picture shows, the wavelength of visible light is about the size of single-celled organisms. On the large end of the scale, radio waves are measured from meters on up to hundreds of meters, while gamma rays are measured in millionths of a nanometer. This is a difference of FIFTEEN orders of magnitude – 15 zeroes from largest to smallest. The EM spectrum is simply gargantuan. And for all of recorded astronomy, from 1610, when Galileo first turned his telescope to the skies, until the 1960s, for 350 years, all of the information we got from the rest of the universe was solely through that tiny slice of the spectrum.
Only since the Sixties have we started to view the universe in other parts of the EM spectrum. First, from ground-based radio telescopes, as radio is one of the very few parts of the EM spectrum that is able to penetrate the earth’s atmosphere. But because radio waves themselves are so large, the resolution that radio telescopes are able to achieve is limited. Your eye has about 7mm of aperture (or maybe just 5mm, if you’re middle-aged, like me) to see light that is at a wavelength that is 10,000,000 times smaller. Amateurs use telescopes with 10 and 50 times more aperture than their eyes to increase that ratio to 100,000,000 and 500,000,000 with corresponding increases in detail to match. Professional observatories continue this march of aperture to increase the ratio to as high as even 100,000,000,000.
On the radio end of the EM spectrum, radio waves vary in size from a few meters to a hundred meters or more. A 100-meter radio dish can only collect radio waves that are less than 100 times smaller than its diameter, so that a view of the sky in the radio spectrum is incredibly blurry, indeed. The largest radio dish on earth has just been completed in China, and is “only” 500 meters across. The resolution of that telescope is much poorer than someone who wears thick coke-bottle glasses can see the sky – without their glasses.
In the Eighties, as our rocketry expertise grew and we were able to launch satellites above the atmosphere, we were able to view the universe in infrared, ultraviolet, microwave, x-rays, and gamma rays. One of the first major space telescope successes was the Infrared Astronomy Satellite, IRAS, launched in 1983. Most infrared wavelengths do not make it down to the earth’s surface, and IRAS performed a full-sky survey in the ten months it was operational in the infrared band. Infrared is the part of the EM spectrum that represents heat. Soldiers use it at night to see heat in those green-hued images you’ve undoubtedly seen.
The infrared wavelength is critical, crucial to our understanding of the universe, because normal interstellar dust blocks visual wavelengths. Visually, we can only see so much, see so far, before the visual wavelength is dimmed or eevn completely blocked by all this dust. However, at infrared wavelengths, the telescope can see right through that dust – right through all the nebula and gas clouds out there. To do this effectively, however, it has to be made as cold as possible so that it can see the “heat” emanating from these deep space objects.
So, for example, here is the glorious Horsehead Nebula in visual wavelengths, pretty much as we’ve always seen it:
At visual wavelengths, the Horsehead is what is known as a dark nebula, standing out against the background because it’s darker than its surroundings. It’s embedded in a giant dust cloud, known as the Orion Molecular Cloud Complex – the beautiful red nebula that the Horsehead is in front of.
In addition to visual wavelengths, Hubble has some near infrared capabilities, and was able to use them to take this glorious shot of the Horsehead through all of that dust:
Note how all of the red is just gone! At infrared wavelengths, that type of interstellar “dust” – mostly hydrogen – becomes invisible. Compare the bright triangle of stars just above the head in both pictures to prove that this really is the same region we’re looking at. The James Webb telescope, which will hopefully be launched (after innumerable delays) in 2018, will operate almost exclusively in the infrared, with some reception visually in red and orange as well. It will also be cooled far colder than Hubble, at just 50 degrees Kelvin. 50 degrees above absolute zero. Brrrrr!!! This cooling will allow for a spectacular increase in the Webb’s ability to see detail in the infrared spectrum.
With these wavelengths, we are able to learn more about the universe than ever before. As Dr. Bally explained in his talk, observations in these wavelengths other than visual have confirmed that these huge Molecular Clouds have organic molecules in them. I thought this type of chemistry only occurred within the confines of planets, asteroids, and comets. But no, these are the building blocks for life forming and floating out there in interstellar and intergalactic space.
Another EM wavelength that reaches the ground from space are microwaves. Yes, the same microwaves you use to heat up your food – but also the same microwaves that are used in radar, and used to transmit information over the air from place to place on earth with big dishes. Because microwaves are still relatively small in size (as compared to the size of radio waves, for example), a dish that’s say, “only” 23 or 39 feet across, can collect an awful lot of microwaves, and more importantly, see an awful lot of detail. An array of such dishes can do so at a resolution far surpassing ground-based visual astronomy. It can even do so at a resolution far surpassing the Hubble as well.
And that’s exactly what has happened. They (you know, the ubiquitous “they”) have built a large microwave observatory in the Atacama desert in Chile, appropriately named the Atacama Large Millimeter Array, or ALMA. It’s located there because water vapor does absorb some microwaves, and the Atacama is known as being the driest place on earth. Also, being at 16,000 feet altitude, above most of the earth’s atmosphere, helps as well.
They’ve installed close to 50 dishes of those two sizes, and use them in the same way as the Very Large Array in New Mexico (as seen in the movie Contact) does for radio waves. They’re able to move the dishes up to 9 miles away from each other on tracks, and to combine the data received from all of the various dishes, so as to greatly increase the resolution, the detail possible to be seen.
The level of resolution is 5 times greater, more detailed, than even the Hubble is able to achieve floating in space above the atmosphere. That’s pretty impressive. This level of detail can reveal startling detail that would otherwise be invisible. Details such as a protoplanetary disk:
Because of the incredible level of resolution possible with ALMA, they are able to obtain images such as this – an actual solar system being formed right in front of our, well, not our eyes, but at least in front of our microwave dishes. At the center of the disk is a young star, called HL Tauri, about 450 light years from earth, in the Taurus Molecular Cloud. And by young, I mean very young – it is estimated to be only about 100,000 years old, just beginning its life of nuclear fusion. The gaps in those rings represent clumping of the dust to form protoplanets, estimated to be about the size of Saturn.
Pretty incredible stuff! As the apocryphal old Chinese proverb/curse states, “May you live in interesting times.” We certainly are.