For the primary time, astronomers have studied a dead star sitting in the guts of a cosmic graveyard of similarly aged stellar bodies.
The stellar remnant, a white dwarf, lies at the middle of a cloud of stellar wreckage, gas and dirt that astronomers call a planetary nebula. It’s situated within the open star cluster Messier 37, which is around 4,500 light years from Earth. Not only could studying this white dwarf and its surroundings reveal the way it died, almost like examining a cosmic crime scene, nevertheless it could also give astronomers a glimpse at what our own solar system will appear like in around 5 billion years.
That’s because, when the sun runs out of fuel for its intrinsic nuclear fusion processes, it’s going to swell right into a red giant. Its puffed-up outer layers will then swallow the inner planets, including Earth. Then, as its shell of stellar material spreads out and cools, the sun will turn out to be a planetary nebula — which confusingly has nothing to do with planets — and its core will turn right into a fading white dwarf.
The butterfly-shaped Messier 37 is an open cluster of stars; the celebrities inside are thought to have been born from the identical vast, dense cloud of gas and dirt at around the identical time. Meaning, by studying a dead star on this cluster, scientists can get a greater picture of how stars of the identical age (but with various masses) evolve and die.
In this manner, open clusters function the right cosmic lab to check theories of stellar evolution.
Massive stars live fast and die young
To this point, astronomers have only discovered three open star clusters containing planetary nebulas, and the white dwarf stars buried on the hearts of those stellar graveyards have never been studied. Before now, that’s.
“The celebs in a cluster are all the identical age; that has a special significance for astrophysics,” Klaus Werner, study team leader and a professor on the University of Tübingen, said in an announcement. “The more massive a star is, the faster it consumes its nuclear fuel by fusing hydrogen into helium. So its life is shorter and it evolves right into a white dwarf faster.”
A part of the stellar process that isn’t yet fully understood is the speed at which stars lose mass before hitting their white dwarf phases, with the connection between a star’s birth mass and death mass called the “initial-final mass relation.” In other words, the mass of a white dwarf may be directly connected to the mass of the star that died to create it. Stars like our sun lose slightly below half their mass by the point they’ve evolved into white dwarfs. Stars with eight times the mass of the sun lose about 80 percent of their mass,” Werner explained. “The information from very young white dwarfs are particularly precious, as these are the central stars of planetary nebulas.”
Werner added that not one of the dead central stars of planetary nebulas have been studied before because they’re all very distant and, as white dwarfs, are also very faint. The team rectified this by training considered one of the planet’s largest telescopes — the Gran Telescopio Canarias on the island of La Palma within the Canary Islands — on the cosmic graveyard in Messier 37.
They then assessed the white dwarf’s light output and determined that it currently has around 85% of the mass of the sun. This means the star that died to go away behind this stellar remnant had a mass such as 2.8 times that of the sun. It also means, based on Werner, that the star lost 70% of its matter during its lifetime.
Moreover, the team was capable of determine the chemical composition of the white dwarf in Messier 37, finding it to strangely lack hydrogen on its surface. This means it was involved in some type of violent event in its past, akin to a transient burst of nuclear fusion — something white dwarfs may undergo when stripping material from a binary companion and pulling it closer.
A greater understanding of the initial-final mass relation is significant to decoding how long a star will live, and whether its final phase might be a white dwarf, a neutron star — or possibly, a black hole. The connection may also help determine if a star in its death throes will trigger a supernova, thereby spreading all the material it has forged during its lifetime out into the universe. That material would then turn out to be the constructing blocks for the following generation of stars.
“Latest generations of stars are formed from the ejected matter, enriched in heavy elements as products of nuclear reactions,” Werner concluded. “That is what the chemical evolution of galaxies — and ultimately all the universe — depends upon.”
The team’s research was published on Oct. 11 within the journal Astronomy & Astrophysics.