How Are Stars Born?

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Stars form from collapsing clouds of gas and dust.

Astronomers can train telescopes on giant clouds of hydrogen gas in our own galaxy and find knots of denser, colder gas and dust that are in the process of giving rise to stars. These dust-thick regions of star birth are often dark and opaque. The Eagle Nebula, depicted in one of the Hubble Space Telescope’s most famous images, is a stellar nursery, but what we see of it in visible light looks like dense cloud pillars.

In 2015, Hubble revisited the Eagle Nebula to create two new images of that famous region—one capturing visible light and the other near-infrared light. In the near-infrared image, the pillars are transformed into ghostly outlines, and hidden stars blaze forth from both within and beyond. Newborn stars shine dramatically from within the cloud.

The Eagle Nebula images provide a striking indication of the difference between what visible-light telescopes like Hubble see and what infrared telescopes like the James Webb Space Telescope can show us. Webb is capable of imaging even further infrared wavelengths of light than Hubble, revealing more of the hidden universe.

Infrared light, unlike visible light, can travel through dust clouds, and instruments that can capture it can see through such clouds as though they were nearly invisible. Webb’s cameras can also detect the infrared glow of the dust and gas, allowing us to learn what it’s made of, how hot and dense it is, and what chemical processes have affected it. These abilities make Webb a critical tool for learning just how star formation works within those dusty depths.

Eagle Nebula visible and ifrared light
Hubble captured the Eagle Nebula in visible light (left) and near-infrared light (right) in 2015. While the visible-light image shows opaque clouds, infrared light penetrates gas and dust, revealing both stars behind the nebula and those hidden inside the pillar. Credit: NASA, ESA, and the Hubble Heritage Team (STScI, AURA). GET THE FULL IMAGE IN RESOURCE GALLERY >

Seeing Stars

Westerlund 2 cluster of young stars in our Milky Way Galaxy
This young cluster of about 3,000 stars in our Milky Way is called Westerlund 2 and contains some of the galaxy’s hottest, brightest, and most massive stars. Hubble’s near-infrared vision pierced dust around this stellar nursery to reveal the dense concentration of stars in the central cluster. Credit: NASA, ESA, the Hubble Heritage Team (STScI, AURA), A. Nota (ESA, STScI), and the Westerlund 2 Science Team. GET THE FULL IMAGE IN RESOURCE GALLERY >

Astronomers know collapsing clouds have a point of no return, when they become so dense and cold that they cannot avoid collapsing under their own gravity. Above this threshold stars form, below it they don’t. But the gas drifting between stars isn’t dense enough by itself to trigger star formation.

Many questions remain about the star formation process; is it triggered mainly by shockwaves from exploding stars, or the pressure created by radiation and stellar winds from massive stars? Or do those processes actually get in the way of the collapse? Alternatively, could star formation begin with the collision and accumulation of sparse pockets of dust and gas? Do stars compete for material in the cloud or do they form mostly in isolation? 

With its powerful infrared sensitivity and resolution, Webb is capable of peering into star-forming regions across the entire Milky Way galaxy, where previous infrared telescopes were limited to dust clouds within our own galactic neighborhood. Webb will provide an unprecedented array of star-formation regions for astronomers to compare and contrast in their search for answers.

Last Updated: May 31, 2018

Keywords:  StarsStar Forming RegionsNebulae

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