Are Barred Spirals Doomed?

The Royal Astronomical Society, London, announced this month that barred spiral galaxies have populations of stars that are closer to the end of their lives than have spiral galaxies without bars. Or as the society summarized in the headline of its Nov. 9 press release: “Bars kill spiral galaxies.”
The study’s methods were a little unorthodox, relying on an “army of volunteers”, in an effort called Galaxy Zoo 2. Mike Tracey, one of the volunteers, was quoted by the society as saying, “I had fun doing my bit and my high school students were involved too. It is great to be part of a real life project which can produce real science.”

Nobody can deny that amateur astronomers have made important contributions to science, and this may be one.
Zooers were asked to pore through photographs of 13,665 galaxies in a group sampling and decide which have bars, and among those with bars, which are reddish or bluish. A bar is a straight formation that cuts through the center of a spiral galaxy, present in about half of all spirals.

Making the distinction can be challenging; when I studied the example the society presented as a blue spiral without a bar, a small bar seemed to show at the center.
“Bars are important for the evolution of galaxies as they provide a way to move material in and out in the disk and possibly help to spark star formation in the central regions,” the Royal Society says. “They may even help feed the central massive black hole that seems to be present in almost all galaxies. But bars provide us with a great puzzle because we still don’t understand why some galaxies have bars and others do not.”
Overall color made a difference because it is important to know the proportion of red, or older, stars versus hot new blue stars. When our sun reaches old age it will become a red giant and puff off its atmosphere, with the gas possibly enveloping Earth. (Presumably the volunteers took account of the phenomenon of red shift, which causes more distant, and receding, objects to appear redder.)

Red spirals are about twice as likely to host bars as are blue spirals, the study found. “The astronomers conclude that bars might help to kill spiral galaxies, although how they do it remains a mystery. But the Milky Way has a bar too, so this discovery may be telling us something about its future,” the Royal Society adds.
Assuming nothing is wrong with the Galaxy Zoo 2 methodology, and assuming the finding is correct, this is an exciting discovery that deserves follow-up by professional observatories. If galaxies were formed around the same period, then age alone can’t account for the change from young blue stars to old red stars. Somehow, a bar pumping energy through the vast conglomeration of star systems might be the reason certain galaxies have more stars nearing the end of their lives.
A week before the study was released I was busy photographing a beautiful barred spiral, NGC925, from the vicinity of Knolls, Tooele County.
I had driven more than an hour west on Interstate 80 to get away from Salt Lake City’s air glow. I intended to set up just outside the Bureau of Land Management’s Knolls Recreation Area (I am not going to pay a recreation fee to do astronomy), but a couple had already claimed that spot. They said they were spending the night. They had gathered firewood for a huge blaze. Anxious to avoid light pollution, I drove off in search of another site.
I found an unused concrete driveway to a fenced-in fiber optic relay station. Its flat surface was a great spot to set up. But as soon as I was irrevocably committed, with tripod aligned and telescope about to settle in, the night darkened and an automatic light went on above the station’s door. It was brilliant yellow, only a few yards from my telescope.
It didn’t take long to find my target, NGC925. According to the NASA/IPAC Extragalactic Database, the galaxy is 10.5 arc-minutes by 5.9 arc-minutes. It is tilted 57 degrees, so we don’t see it face on. The database lists its magnitude as 10.69. This island universe is part of a cluster of at least 11 galaxies, the NGC1023 group.
Using measurements taken by the Large Azimuthal Telescope in Russia’s Caucasus Mountains as well as by the Hubble Space Telescope, astronomers N. A. Tikhonov and O. A. Galazoutdinova determined the galaxy is 28.4 million light-years away. Their report was published in 2002 in the journal Astrofizika, based in Yerevan, Armenia.
Using a pocket knife, I sliced off a piece of a rubber mat; I taped it to my telescope to shield the instrument from the light as best I could. It didn’t block the bonfire’s blaze or the light from vehicles rumbling past on I-80, but those were insignificant contributors to the glow.

I spent the night of Nov. 3-4, 2010, taking views. Here is the result.

[Photo of barred spiral galaxy NGC925 that I took at Knolls, Tooele County, the night of Nov. 3-4]

Studying this mysterious, distant object, I have to wonder whether the prominent bar structure will lead to the demise of many of its stars. What’s going on?

Leave a comment

DeseretNews.com encourages a civil dialogue among its readers. We welcome your thoughtful comments.

*