Every day the sun rises and sets. It’s always constant. But it won’t always be. As stars like our sun get into the later stages of their lives, they undergo drastic changes. Billions of years from now our sun will swell to an enormous size. Life on Earth will end as the sun’s expansion swallows our planet.
Something else happens at this late stage. Stars begin to pulsate. Their brightness sees massive swings as it increases and decreases every few hundred years. Astronomers have observed many of these stars pulsating in our galaxy. What about other galaxies? That’s what a team of astronomers from Yale and the Harvard-Smithsonian Center for Astrophysics went searching for.
“We realized that these stars are so bright and their pulsations so strong, that they are difficult to hide,” said Charlie Conroy, an assistant professor at Harvard University and astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), who led the research. “We decided to see if the pulsations of these stars could be detected even if we couldn’t separate their light from the sea of unchanging stars that are their neighbors.”
M87 was their target. It’s a massive elliptical galaxy located about 53 million light-years from Earth. It’s best known for a large number of globular clusters – about 12,000 compared to the 200 orbiting the Milky Way.
Here’s what they found after studying a series of images taken by the Hubble Space Telescope in 2006.
“Amazingly, one in for pixels in the image changes with time,” said Peter van Dokkum, a professor and chair of the astronomy department at Yale University. “We tend to think of galaxies as steady beacons in the sky, but they are actually ‘shimmering’ due to all the giant, pulsating stars in them.”
Conroy describes the regular changes in brightness as a heartbeat. “It’s as if we’re taking the pulse of the galaxy,” said Conroy.
Using the pulse to determine age
Using these stellar heartbeats, astronomers have a new way of measuring how old a galaxy is. By looking at the strength and speed of the galaxy’s pulses, astronomers can determine a galaxy’s age. This new technique shows M87 is about 10 billion years old, which lines up with previous estimates using different techniques.
What’s next? Every galaxy should show similar pulsing patterns. The team of astronomers aims to use their technique on other galaxies. “Our models suggest that the pulsations will be stronger in younger galaxies, and that’s something we’d love to test,” said Jieun Choi, co-author of the study.
Don’t expect M87 to code blue anytime soon. Van Dokkum says the galaxies have about a trillion more years ahead of them.
How to see M87
It’s not every day you can see a galaxy talked about by astronomers. Most astronomers tend to study smaller or more distant galaxies. M87’s apparent magnitude of 9.59 makes it an easy target for anyone who owns a small telescope. M87 calls the Virgo constellation home.
(Image from Sky Guide app)
The best time to see it right now is a couple of hours before sunrise.