Carina Nebula survey offers insight into how sun was formed

A new survey of Carina Nebula, one of the most active star-forming regions in the galactic neighborhood, is helping astronomers better understand the processes that may have contributed to the formation of the sun 4.5 billion years ago.

Lead author Patrick Hartigan of Rice University said that most stars form in giant molecular clouds, regions where the density of matter is sufficient for hydrogen atoms to pair up and form H2 molecules, adding that the Carina Nebula is an ideal place to observe how this happens because there are dozens of examples of forming stars at various stages of development.

The Carina Nebula spans more than 100 light-years and is visible to the naked eye as a bright glowing patch in the Milky Way for observers in the Southern Hemisphere. In addition to thousands of stars similar in mass to the sun, Carina contains more than 70 O-type stars, each with a mass between 15 and 150 times that of the sun. O-stars burn hot and bright and die young, typically within 10 million years. These massive stars play a key role in how less-massive, solar-type stars in the same region evolve because O-stars evaporate and disperse dust and gas that might otherwise collect in a disk to form planets around the low-mass stars.

Hartigan said that ultraviolet radiation from these hot, massive stars ionizes molecular hydrogen, and as the radiation evaporates the molecular cloud, O-stars carve beautiful pillars and clear the space around smaller stars that exist nearby.

Hartigan added the sculpting process that creates such pillars marks one stage of the destruction of a molecular cloud. In the first stage, the outer wall of the cloud appears largely unbroken. Fat pillars form first and are steadily eroded into skinny pillars that eventually become isolated globules that are disconnected from the receding wall. Often, a young star with a disk is present at the apex of a pillar or within a globule. The entire evaporation process takes about a million years, and astronomers believe it is an essential aspect in the creation of solar systems like our own.

The Carina star-formation region is about 7,500 light-years from Earth, about five times farther away than the Orion Nebula, which is visible in the northern hemisphere but is only about one-tenth the size of the Carina Nebula.

Hartigan said numerical simulations in recent decades have suggested that strong stellar winds from O-stars also induce star formation by compressing material in a molecular cloud to the point where it becomes gravitationally unstable, a process known as triggering. He said the new images reveal important constraints on this process.

The survey is available online in the Astronomical Journal.