May 27, 2018
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Amateur Naturalist: Red dwarfs are like giants of sand on beaches

Hubble Space Telescope photo courtesy of NASA/ESA/E. Peng (Beijing University)
Hubble Space Telescope photo courtesy of NASA/ESA/E. Peng (Beijing University)
NGC 4458, a galaxy in the Virgo cluster of galaxies. The smaller swatches of light are also galaxies.
By Dana Wilde, BDN Staff

Do you see nothing there?
Nothing at all; yet all that is I see.
– Hamlet, III. iv.

It was only in 1924 that anyone knew for certain there were any galaxies other than ours. That was less than 100 years ago, mind you, when Edwin Hubble was taking what we consider now to be pretty grainy pictures of light swatches to prove there were Milky Ways beyond the Milky Way.

How many galaxies there were, of course, was not known or, as far as I know, even imagined. In a later incarnation of a star count, Carl Sagan in the early 1980s grandly explained that there are more stars in the universe than there are grains of sand on the beaches of the Earth. Sagan died in 1996, and by then the Hubble Space Telescope’s much clearer photos were further cleansing our perception of heaven’s deeps. The estimates of how many galaxies there might be expanded from one in 1924 to 100 billion by around 2000. Some astronomers are thinking nowadays there could be 170 billion galaxies out there.

A galaxy is a group of stars. Small galaxies have around 10 million stars, the hugest have as many as 100 trillion stars, and middle-sized galaxies like our Milky Way have maybe around 400 billion stars. One of our satellite galaxies, the Large Magellanic Cloud, has around 10 billion stars. Galaxy M31, which is near enough to see with binoculars on autumn nights as a fuzzy patch of light, has around 1 trillion stars. A rough estimate a few years ago was that altogether there were around 100 billion trillion stars in the universe our instruments allow us to see.

Then last year, some astronomers at Yale figured out there are a lot more red dwarf stars than anyone ever thought. Red dwarfs are small stars that are so dim they can’t actually be seen from here and inhabit galaxies like ghosts. And they’re so slow-burning that the universe – currently thought to be 13.7 billion years of age – has not existed long enough for any of them to expire. The astronomers, who detected signs of them in light spectra from some large elliptical galaxies, concluded that red dwarfs account for around 60 percent of the star-mass in those galaxies. If ghosts like these haunt galaxies generally, then it means there are roughly triple the number of stars previously thought –  meaning that, in the universe we perceive, there are about 300 billion trillion stars. One astronomer trying to figure out what Carl Sagan was talking about estimated there are about 2,000 billion billion grains of sand on Earth.

These are just estimates, based on what we see now. There is of course no elusive “actual number” of stars in the universe because stars are perpetually coming into and going out of existence, like people. Stars are born in stellar ignition fields and die millions or billions of years later by fading away or exploding, and some, like red dwarfs, burn low and walk the night unseen practically forever.

In a clear, dark sky from our grain of sand, you could, if you set your mind to it, count about 6,000 stars. With binoculars you can see a lot more. Most of them are in our galaxy. Out beyond that, it’s an undiscovered country. The best scientific instruments, and theories, account for only about 4 percent of all that is apparently out there. Like galaxies, there are more red dwarfs than was ever dreamed of in our cosmology, and who knows what else will come through the door to haunt us if our perceptions are ever fully cleansed?

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