StarDate

A wave of starbirth is sweeping through Scorpius and some nearby constellations. It started about 20 million years ago, and is continuing today. It’s triggered the birth of thousands of stars, including some of the most impressive in our part of the galaxy.

The complex is called the Scorpius-Centaurus association. It consists of three distinct regions that appear to be related. Giant clouds of gas and dust in one of those regions began collapsing tens of millions of years ago. That gave birth to the first stars in the association.

The most massive members of that group produced winds and radiation that squeezed the surrounding clouds. And some of those early stars exploded, creating shockwaves that compressed the clouds even more. That triggered the birth of many more stars.

Many stars in the association are extremely big, bright, and massive. They account for many of the bright lights that outline the scorpion, the centaur, and other constellations in the region. For every one of those stars, there are hundreds of less-massive stars.

From Earth, the most impressive member of the association is Antares, the heart of the scorpion, which is quite near the Moon tonight. Antares is more than a dozen times the mass of the Sun, and tens of thousands of times brighter. In the next million years it’s likely to explode as a supernova – perhaps triggering the birth of even more stars in this busy complex.

Script by Damond Benningfield

Two stars that sound a bit scary peek above the southern horizon on summer nights. Together, they form the “stinger” – the end of the curving body of the scorpion.

The stars are Lambda and Upsilon Scorpii. Lambda is the brighter of the two. It’s also the more complicated – it consists of three stars.

The system’s details are a bit uncertain. That’s largely because its distance is uncertain. Estimates range from about 365 light-years to almost twice that range. Without a good measurement of the distance, it’s tough to figure out how big and heavy the stars really are.

We do know that the system consists of a tight binary – two stars that orbit each other once every six days – plus a third star that orbits the others every three years.

One of the stars in the binary is much bigger and brighter than the Sun, and 10 to 14 times the Sun’s mass. That means the star will end its life with a colossal explosion.

Its close companion is maybe twice the mass of the Sun. But it’s not yet fully formed. The distant companion is another big guy – roughly 8 to 10 times the mass of the Sun. If it’s at the high end of that range, then it, too, will explode as a supernova. If not, its fate is less certain. It could become a supernova, but it also might expire in a more gentle process – a fate similar to the Sun’s.

More about the scorpion tomorrow.

Script by Damond Benningfield

A star system on the far side of the galaxy keeps blowing up. Since 1863, astronomers have recorded 12 outbursts from the system – the most recent just four years ago. The flare-ups are powered by a complicated interplay between a dead star and a companion that may be dying.

U Scorpii probably is more than 60,000 light-years away, far on the other side of the heart of the Milky Way Galaxy. Most of the time, the system is quite faint. But during the outbursts, it can flare 10,000 times brighter in just a few hours. It starts to fade quickly, but it takes about two months to return to its “quiet” state.

The system consists of two stars in a tight orbit. One of them is a white dwarf – the dead core of a Sun-like star. The other star is headed toward the same fate. It’s at the end of the prime phase of life, so it’s starting to puff up. The white dwarf “steals” some of the gas from its surface, forming a swirling disk.

Some of the gas piles up on the white dwarf. Eventually, the gas gets so hot, it sets off a nuclear blast, making the system flare up. The outburst blows away all or part of the disk. Before long, though, the process starts all over again – leading to another explosion a few years later.

U Scorpii is in Scorpius, which is low in the south-southeast at nightfall. The system is above the curving line of stars that outlines the scorpion’s body and tail.

Script by Damond Benningfield

About 10,000 light-years from Earth, a dead star is devouring its living companion. The process creates a disk of gas that’s heated to millions of degrees, so it shines brightly. Some of the gas is fired back into space at almost the speed of light, adding to the fireworks. The system is so powerful that it’s classified as a microquasar – a smaller version of some of the brightest objects in the universe.

GRO J1655-40 consists of a black hole about six or seven times the mass of the Sun, plus a close companion star more than twice the Sun’s mass.

The black hole probably began as a star about 25 times the Sun’s mass. It evolved quickly, with its core collapsing to form the black hole. Its outer layers were blasted into space. Some of that material fell on the companion. Today, the black hole is pulling some of that gas away from the companion.

The same thing happens in the cores of many remote galaxies. Supermassive black holes create monster disks as they pull in gas, dust, and stars. Such a disk can shine billions of times brighter than the Sun – forming a quasar. GRO J1655-40 is a smaller version of that.

The system is in Scorpius, which crawls across the south on summer evenings. The microquasar is near where the scorpion’s body curves to form its tail.

Script by Damond Benningfield

It’s hard to see a pattern in most of the constellations. Their stars are too faint or too spread out, or the pattern is just too obscure. Perhaps the most prominent exception is Scorpius. It takes little imagination to see the curving body of a scorpion in its stars.

The scorpion skitters low across the south on summer nights. Its brightest star is Antares. The scorpion’s body and tail curl to the lower left. The head is to the upper right. It’s marked by a line of three stars. They’re about the same brightness, and they’re fairly evenly spaced.

From top to bottom, the stars are Beta, Delta, and Pi Scorpii. Delta is a bit brighter than the others.

All three stars are extraordinary. Each of them actually consists of more than one star. All of the member stars are quite young – no more than a few percent the age of the Sun. And most of them are big and heavy, with some of them fated to end their lives as supernovas – titanic explosions that will outshine billions of normal stars.

Delta Scorpii consists of two stars. At least one of them will become a supernova. Pi Scorpii is a triple system. It also features at least one future supernova.

Beta is the busiest of the systems – at least six stars, all orbiting each other in a complex gravitational ballet. Two of those stars are likely to become supernovas – briefly highlighting the head of the scorpion.

Script by Damond Benningfield