Astronomers have discovered a tiny, rapidly rotating neutron star that appears to be murdering a companion sun in a case of celestial fratricide that promises to shed light on stellar evolution and death.
The "eclipsing millisecond pulsar," the massive remnant of an exploded sun, and its companion white dwarf star are located in Terzan 5, a globular star cluster near the center of the Milky Way galaxy at a distance of some 24,000 light years.A light year is the distance light, traveling at 186,000 miles per second, travels in one year. Terzan 5 is so far away that light, or radio energy, takes 24,000 years to reach Earth.
The newly discovered pulsar, known as PSR 1744-24, and its white dwarf companion whirl about each other every 109 minutes at a distance of just 18,600 miles - about one-13th the distance from the Earth to the moon, according to a letter published Wednesday in the British science journal Nature.
The pulsar, about 6 miles wide, has 1 1/2 times the mass of Earth's sun. The white dwarf, a small star in the final stages of its life, is about the size of the Earth. The two stars are so close to each other that the pulsar's intense radiation is blowing away the atmosphere of the white dwarf.
The pulsar is "irradiating it with a very hard, energetic radiation," said Miller Goss of the Very Large Array telescopes at the National Radio Astronomy Observatory in New Mexico. "It's just boiling it away.
"It's going to cause this poor little star, the one that's being murdered, to disappear someday; it's just going to evaporate," he said in a telephone interview.
Working with radio telescopes in Australia, Britain and the United States, Goss and other astronomers were able to determine the nature of the strange binary star system by studying intermittent radio signals from the pulsar.
Because of the periodic nature of the signals, scientists concluded that the pulsar and another star were in orbit around each other and that the companion star periodically blocked the radio signals from the pulsar as seen from Earth.
How fast two objects orbit each other is a function of their mass and the distance between them. Repeated observations allowed astronomers to compute the orbital parameters of the Terzan 5 pulsar.But the eclipses of PSR 1744-24 are extremely variable and "there is no doubt that the eclipses are due to a wind emanating from the companion," the scientists wrote.
PSR 1744-24 is the second such eclipsing pulsar ever discovered. But the stars in the first such duo are much more widely separated.
"In that case, the orbit is about eight or nine hours and the eclipse is only occurring for say 40 or 50 minutes," Goss said. "In this new one, the orbit is a little bit less than two hours and the eclipse is occurring about half the time. And the eclipse is very variable."
PSR 1744-24 is unique "in the sense that the two stars are much closer, by a very large factor," he said. "That's why this very severe eclipsing occurs.
"It's as if this pulsar is existing in kind of the weather of the debris of the other star that it's evaporating."
Studying such a star system will shed insights into how the tightly packed suns in massive globular clusters interact and evolve. "We're learning a lot about stellar evolution and the whole way that stars interact," Goss said.
Spinning neutron stars are known as pulsars because they emit bursts of radiation as they rotate. In the case of PSR 1744-24, radiation bursts occur 100 times per second.