Soundings – Cosmic accident mimics early universe
The Milky Way, the combined glow of billions of stars toward the center off our galaxy, is high overhead when the sky grows dark tonight.
The Milky Way is not uniformly “milky.” Clouds of gas and dust absorb light, making it blotchy.
Left to themselves, a cloud of gas and dust doesn’t do much. But stir it up, and parts of the cloud draw together – pull in more gas and dust – and give birth to stars.
In our galaxy, and in most of the galaxies close to us in space and time, gas-and-dust clouds are rarely stirred up. The present-day universe is not a hotbed of star formation.
The last two stars of the bowl of the Big Dipper are “the pointers.” They point (roughly) to Polaris, the north star. Just off the line between the pointers and Polaris, an astronomer in the late 1700s discovered two fuzzballs.
Whatever they were, they weren’t comets, then a hot topic of research. To alert astronomers not to be distracted by the two new objects, Charles Messier (mess-YAY) a few years later listed them in his catalog of non-comets; they’re now known as M81 and M82.
A hundred years later, in the late 1800s, “Messier objects” were themselves hot topics: What were they? And where were they – within our galaxy, or outside it?
The largest telescope of the day revealed that M82 is not uniform: it’s blotchy – like the Milky Way, it’s rich in gas and dust.
In the 20th century, astronomers developed techniques to study the heavens in electromagnetic wavelengths other than visible light. In the early 1960s, they discovered that M82 was emitting large amounts of radio.
M81 and M82 lie roughly 10 million light years from Earth – close to us in both space and time. A galactic accident, however, has allowed us to glimpse in them what starbirth might have been like in the early universe.
M81 and M82 are today about 120,000 light years from each other, and are steadily moving apart. Three hundred million years ago, they were much closer to each other. Just as Earth and moon raise tides on each other, so, too, did M81 and M82 when they nearly collided. The tides stirred up M82’s clouds of gas and dust, triggering the birth of new stars, turning M82 into a “starburst galaxy” – wave after wave of bright baby stars, quickly burning through their fuel, then exploding as supernovae.
Supernova explosions spew great jets of subatomic particles – broken atoms – into space.
Whenever charged particles accelerate, they emit radio waves (accelerate some electrons now by flipping a light switch; an AM radio held nearby will pick up the resulting radio waves as static).
Starburst galaxies should have been common in the early universe, when galaxies were close, and contained more gas and dust than they do today.
The Hubble Ultra-Deep Field is an image of the early universe, produced when the Hubble stared at one point in space for over a million seconds (at 60 seconds/minute, 60 minutes/hour, 24 hours/day – more than 11 days).
The Ultra Deep field contains images of hundreds of galaxies. Many seem to have been disrupted – not unlike our neighbor, M82.
M82 provides a close-up view of something normally seen only very far away in space and time: a starburst galaxy. We’ll observe M82, and M81 – the fuzzballs discovered centuries ago – in our scopes at the old Nevada City airport, on Saturday, Aug. 7, at 9 PM.
Alan Stahler trained as a biologist and is an amateur astronomer. He teaches enrichment classes for children and adults at Sierra Friends Center. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).
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