Scan of Orion stellar nursery reveals how stars are born

In the sharpest close-up ever, James Webb Space Telescope (JWST) has revealed the germination, growth and birth of stars in the closest stellar nursery, the Orion nebula.

Located in the constellation Orion, about 1,350 light-years away from Earth, the Orion nebula, also known as Messier 42 (or M42 for short), is a gigantic cloud with a mass 2,000 times the mass of the Sun. The Orion gas cloud is enormous; it is 24 light-years across, meaning light takes about 24 years to travel from one edge to its opposite.

Orion nebula appears as a spot of cloud to the naked eye on a moonless dark night. Even crude telescopes show rich details, and astronomers have known it to be a star-forming region. The ambience in this enormous bubble of gas and dust is similar to the environment that prevailed in the solar system around 4.5 billion years ago when the Sun and the planets evolved. All giant telescopes have studied this region, including Nasa’s Hubble. However, dust and gas block the visible light from the budding star-forming areas. Hence they have remained obscured from our observation until now.

While opaque to visible light, gas and dust are transparent to infrared rays. Armed with NIRCam (Near Infrared Camera), James Webb Telescope peered deep into the star-forming regions of the Orion nebula. The image obtained on September 11 by the JWST reveal unprecedented details of the nebula, showing details with much greater clarity than in any previous pictures of this region.

The interstellar space between stars is not a perfect vacuum devoid of material. There is just about one atom in one cubic centimetre, a volume equivalent to a typical sugar cube. However, in the regions such as the Orion nebula, the density is about a thousand atoms per cubic centimetre. Nonetheless, how such a near vacuum collates and coalesces into a star with a typical density of about a hundred septillion (one followed by 26 zeros) during the first million years of stellar evolution is still a mystery.

By comparing the scans at different stages of pregnancy, one can fairly put together the picture of the growth of the foetus. Likewise, the JWST has revealed newborn stars at various stages of their development in the Orion nebula.

1) Filaments

Theta Orionis, also known as ‘the Trapezium’, a cluster of four young stars, is at the heart of the Orion nebula. The stars, located in the direction of the top right, are not visible in this image. The strong stellar wind (consisting of fast-moving ionised particles) and ultraviolet rays from these stars create turbulence and whip-up filament-like structures. Swept by the powerful winds, the filaments attain a typical density of about a million atoms per cubic centimetre, kick-starting the star formation.

As more and more matter condenses, the combined gravitational attraction becomes more vigorous. Gobbling up the matter from the surrounding regions, these spots grow and become larger and denser. Inset 1 in this image shows thin, meandering filaments especially rich in hydrocarbon molecules and molecular hydrogen sculpted by the stellar winds blowing from the stars of the trapezium cluster.

2) Formation of the protoplanetary globule

Like water flows downhill, matter from the surrounding region falls towards the high-density spots in the filament. The accreting matter, larger than the size of the solar system, with a density of about trillion atoms per cubic centimetre, evolves into stars and planets. Inset 2 is a young star called HST-10, with planet-forming disks of gas and dust around it. The intense radiation from the Trapezium cluster creates this cocoon of dust and gas around the newly emerging star. The clouds of dust and gas around the protostar are bigger than the solar system. Look at the size of the orbit of Neptune shown for comparison. The centre of this cocoon is likely to eventually emerge into a star, and the gas and dust around it would coalesce into planets. Astronomers have spotted about 180 photoevaporating disks (globules of gas shaped by the radiation from the nearby stars) around young stars (aka Proplyds) in this bustling stellar nursery. Not all such globules emerge into stars. The intense radiation from the nearby stars could sweep away the materials. The remaining mass may be comparable to the mass of Jupiter and may become failed stars.

3) Protostar

With more mass accreting, given time, the density reaches about one septillion (one followed by 22 zeros) atoms per cubic centimetre. Inside, the great globs of gas slowly collapse into stellar embryos. The density gradually grows to about 100 septillions. Such a gas disc’s centre becomes dense and hot enough to trigger thermonuclear fusion. As the hydrogen atoms fuse to become helium, energy is released at its core- they start to shine. The radiation from the star mops away the dust and gas around it, and the star comes out and blazes bright. Inset 3 above is a stellar embryo inside a globule of dust and gas. It is still in the process of formation, and it has not to have had time to fling away its natal cocoon of gas and dust surrounding it.

4) Neonatal star

In inset 4 above is the newborn star θ2 Orionis A formed just a million years ago. The star is very young compared to Sun, which is 4.6 billion years old. Nonetheless, the radiation from the star has cleared the cocoon of dust and gas in which it birthed. Hundreds of such young stars abound the Orion nebula.

The eyes of the JWST are so sharp that it can spot structures of the order of 0.0006 light-years (or about 5 light hour distance, typically the size of a solar system). This has enabled astronomers to spot several star-forming regions.

The image, a composite created by stacking multiple photos taken with several different filters, was put together from various observations by an international team of 100 scientists from 18 countries belonging to many institutions such as the French National Center for Scientific Research (CNRS), Western University in Canada, and the University of Michigan.