NASA discovers five 'superstars' in other galaxies

Scientists have found five objects in other galaxies similar to Eta Carinae - the most luminous and massive stellar system within 10,000 light years of Earth - using data from NASA's Spitzer and Hubble space telescopes.
Eta Carinais best known for an enormous eruption seen in the mid-19th century that hurled an amount of material at least 10 times the Sun's mass into space.
This expanding veil of gas and dust, which still shrouds Eta Carinae, makes it the only object of its kind known in our galaxy.
A new study using archival data from NASA's Spitzer and Hubble space telescopes has found five similar objects in other galaxies for the first time.

"The most massive stars are always rare, but they have tremendous impact on the chemical and physical evolution of their host galaxy," said lead scientist Rubab Khan, from NASA's Goddard Space Flight Centre in US.
These stars produce and distribute large amounts of the chemical elements vital to life and eventually explode as supernovae.

Located about 7,500 light-years away in the southern constellation of Carina, Eta Carinae outshines our Sun by 5 million times, the researchers said.
The binary system consists of two massive stars in a tight 5.5-year orbit. Astronomers estimate that the more massive star has about 90 times the Sun's mass, while the smaller companion may exceed 30 solar masses.

Catching rare stars during the short-lived aftermath of a major outburst approaches needle-in-a-haystack levels of difficulty, and nothing matching Eta Carinae had been found prior to the study.
The researchers developed a kind of optical and infrared fingerprint for identifying possible Eta Carinae twins, or "Eta twins" for short.
Dust forms in gas ejected by a massive star. This dust dims the star's ultraviolet and visible light, but it absorbs and reradiates this energy as heat at longer, mid-infrared wavelengths.
"With Spitzer we see a steady increase in brightness starting at around 3 microns and peaking between 8 and 24 microns," said Khan.

"By comparing this emission to the dimming we see in Hubble's optical images, we could determine how much dust was present and compare it to the amount we see around Eta Carinae," he said.
The researchers found two candidate Eta twins in the galaxy M83, located 15 million light-years away, and one each in NGC 6946, M101, and M51, located between 18 million and 26 million light-years away.
These five objects mimic the optical and infrared properties of Eta Carinae, indicating that each very likely contains a high-mass star buried in five to 10 solar masses of gas and dust.

The study was published in The Astrophysical Journal Letters.