Throughout our Milky Way Galaxy, more than 100 groups of stars known as globular clusters have been found. They are thought to be the oldest groupings of stars in the galaxy, having formed shortly after the Big Bang, when the galaxy as a whole was created.
Scientists believe that determining the age of globular clusters would help tackle that unsolved Big Question: How old is the Universe?
Researchers at the European Southern Observatory recently inched a step closer to answering the Big Question when they confirmed the existence of some small, hot objects called white dwarf stars in a globular cluster known as NGC 6397, then calculated the temperature and mass of the stars.
By pinning down the properties of these tiny stars, researchers say they can now estimate the distance to the globular cluster in which they reside. At an estimated 8,000 light years away, the four white dwarf stars are the most distant ever confirmed to exist.
Knowing distance allows for a calculation of age, and since globular clusters are thought to be the oldest stellar groupings around, their age would represent a lower limit to the age of the Universe, now thought to be between 12 and 16 billion years.
Teaspoons and elephant
White dwarf stars are typically about the size of Earth, but their mass is often equivalent to the sun -- making for objects that are a million times more dense than the sun. A teaspoonful of a white dwarf, if brought to Earth, would weigh as much as an elephant.
While extremely large stars typically end their lives in a dramatic explosion, called a supernova, white dwarf stars are the end of the evolutionary road for smaller stars, ones which never had a high enough central pressure or temperature to trigger thermonuclear reactions.
When a star the size of our sun or smaller nears the end of its life, it sheds its outer layers, leaving behind a burned-out core. With no internal energy source left, the small, dense star radiates leftover energy, like dying embers, and gradually cools. Meanwhile, the surfaces can exceed 90,000 Fahrenheit (50,000 C). The surface of our sun is about 9,980 Fahrenheit (5,527 C).
The first white dwarf was discovered in 1862. It is a companion to Sirius, the brightest star in the sky. More recently, the Hubble Space Telescope had found evidence of white dwarf stars in globular clusters (see the accompanying image).
Using the ESO's Very Large Telescope at the Paranal Observatory in Chile, an international group of astronomers led by Sabine Moehler obtained detailed spectral data confirming the existence of the four white dwarf stars in NGC 6397. The brightest of the four stars, named WF4-358, has a surface temperature of about 32,430 Fahrenheit (18,000 C) and a relatively low mass -- about one-third that of our sun.
The ongoing study, which will attempt to refine the existing data and collect information on more white dwarf stars, has been submitted to the research journal Astronomy & Astrophysics.
advertisement
