Human lives are just blips on the cosmic time scale, which makes it impossible for us to witness the full life cycles of stars, planets and galaxies. But sometimes, if we're lucky, astronomers might be able to catch crucial moments playing out before their eyes. Now a team from Australia and Hungary have done just that, watching as a red giant star goes through its death throes.
The star in question is called T Ursae Minoris (T UMi), located about 3,000 light-years away in the constellation of Little Bear. At around 1.2 billion years young, the star is only about a quarter the age of the Sun, but because it started with twice the mass it's burned out much faster.
And now astronomers are watching, almost in real time, as it enters its next phase of life. After exhausting its fuel supply a few million years ago, T UMi became a variable red giant, changing its size, brightness and temperature on a semi-regular schedule of pulses.
"Energy production in T UMi has become unstable," says Meridith Joyce, co-lead author of the study. "During this phase, nuclear fusion flares up deep inside, causing 'hiccups' that we call thermal pulses. These pulses cause drastic, rapid changes in the size and brightness of the star, which are detectable over centuries. The pulses of old stars like T UMi also enrich the entire universe with elements including carbon, nitrogen, tin and lead."
And now it looks like this stellar light show is almost over. The team examined observational data of T UMi gathered over the last 30 years, and found that the star seems to be shrinking, dimming and cooling. This indicates that its pulsing period won't continue for much longer, and soon the red giant will shed its outer layers and leave behind a white dwarf.
"We believe the star is entering one of its last remaining pulses, and we'd expect to see it expanding again in our lifetimes," says Joyce. "The star will eventually become a white dwarf within a few hundred thousand years. This has been one of the rare opportunities when the signs of aging could be directly observed in a star over human timescales."
The research was published in the Astrophysical Journal.
Source: Australian National University