By Will Dunham
WASHINGTON (Reuters) – Two large stars residing within a spectacular cloud of gas and dust dubbed the “Dragon’s Egg” nebula have presented a conundrum for astronomers. One of them has a magnetic field, just like our sun. Your partner doesn’t. And these massive stars are not usually associated with nebulae.
Researchers now appear to have solved this mystery, while also explaining how the relatively few massive stars that are magnetic got that way. Stellar fratricide is to blame, they said. In this case, the larger star apparently swallowed a smaller sister star, and the mixing of their stellar material during this hostile acquisition created a magnetic field.
“This merger was probably very violent. When two stars merge, material can be expelled, and this probably created the nebula we see today,” said Abigail Frost, an astronomer at the Chile-based European Southern Observatory and lead author of the study published on Thursday in the journal Science.
Computer simulations previously predicted that the mixing of stellar material during such a merger could create a magnetic field in the combined star born in this process.
“Our study is observational evidence that confirms this scenario,” said astronomer Hugues Sana, from KU Leuven in Belgium, senior author of the study.
These two stars – gravitationally linked to each other in what is called a binary system – are located in our galaxy, the Milky Way, about 3,700 light-years from Earth, in the constellation Norma. A light year is the distance light travels in one year, 5.9 trillion miles (9.5 trillion km).
The researchers used nine years of observations from the Chile-based Very Large Telescope.
The magnetic star is about 30 times more massive than the sun. Its remaining companion is about 26.5 times more massive than the sun. They orbit at a distance from each other ranging from seven to 60 times the distance between the Earth and the Sun.
The Dragon’s Egg is so named because it is located relatively close to a larger nebulous complex called the Fighting Dragons of Ara. The stars inside the Dragon’s Egg appear to have started out between 4 and 6 million years ago as a triple system – three stars born at the same time and gravitationally bound.
The two innermost members of the triple system included a larger star—perhaps 25 to 30 times the mass of the Sun—and a smaller one—perhaps five to 10 times the mass of the Sun.
The more massive one evolved more quickly than the other, with its outer layer swallowing the smaller star and triggering a merger that ejected the gas and dust that make up the nebula into space, researchers said.
This occurred very recently on a cosmic timescale – about 7,500 years ago, based on the rate of expansion of material in the nebula. It consists mainly of hydrogen and helium, but also an unusually large amount of nitrogen, thanks to fusion.
Many Sun-sized stars generate magnetic fields.
“For low-mass stars like our Sun, convective heating – like the movement of hot water in a radiator in your home – creates a movement of stellar material. This, in turn, creates a dynamo effect that induces a magnetic field, ” said Frost.
“However, for massive stars – larger than eight times the mass of our Sun – different heating effects are at play, and so explaining the presence of magnetic fields for these types of stars is more complicated. This merger scenario ticks all the boxes. the requirements.” Frost added.
It is known that about 7% of massive stars have a magnetic field. The second star in this binary system, not involved in the violent merger, does not.
Stellar magnetic fields store immense amounts of energy. The Sun’s magnetic storms can interact with Earth’s atmosphere and create our planet’s exciting auroras, but they can also disrupt radio signals and navigation systems.
An image of the nebula released with the study is visually stunning.
“The richness of physics and chemistry at play gave rise to a beautiful structure,” said Sana.
(Reporting by Will Dunham, Editing by Rosalba O’Brien)
