A cosmic hourglass: Webb captures image of protostar shrouded in dark clouds

The protostar L1527 is embedded in a cloud of material that fuels its growth.

Last month, the James Webb Telescope gave us a spectacular new image of the Pillars of Creation – perhaps the most famous image taken by Webb’s predecessor, the Hubble Space Telescope, in 1995. Now the telescope is giving astronomers clues to the formation of a new star, with a stunning image of an hourglass-shaped dark cloud surrounding a protostar, an object known as L1527.

As we previously reported, the James Webb Space Telescope launched in December 2021 and, after a tense sunshade and mirror placement over several months, began capturing stunning images. First, there was the deep-field image of the Universe, which was released in July. This was followed by images of the atmospheres of exoplanets, the Southern Ring Nebula, a cluster of interacting galaxies called Stephan’s Quintet, and the Carina Nebula, a star-forming region about 7,600 light-years away.

In August, we received beautiful images of Jupiter, including the auroras at both poles that result from Jupiter’s powerful magnetic field, as well as its thin rings and two of the gas giant’s small moons. This was followed a month later by a mosaic image showing a panorama of star formation stretching a whopping 340 light-years in the Tarantula Nebula — so named for its long, dusty filaments. We were also treated to spectacular images of Neptune and its rings, which have not been directly observed since Voyager 2 flew past the planet in 1989, and, as already mentioned, the Pillars of Creation.

This latest image comes from Webb’s primary imager, the Near-Infrared Camera (MIRCam). To capture images of very faint objects, NIRCam’s coronagraphs block out any light coming from brighter objects nearby, similar to how shielding the eyes from bright sunlight helps us focus on the scene in front of us. L1527’s dark clouds are only visible in infrared, and NIRCam was able to capture features previously hidden from view. See:

Enlarge / Material ejected from the star has freed up cavities above and below, the boundaries of which glow orange and blue in this infrared image.


In 2012, astronomers used the Submillimeter Array — a collection of eight radio telescopes arranged in an interferometer that’s also part of the Event Horizon Telescope — to study the accretion disk around L1527 and measure its properties, including its rotation. They found that the disk showed Keplerian motion, just like the planets in our solar system, which allowed them to determine the protostar’s mass. So learning more about L1527 could teach us more about what our own sun and solar system looked like in its infancy.

Protostars are the earliest stage in stellar evolution, typically lasting about 500,000 years. The process begins when a fragment of a molecular cloud of dense dust and gas gains enough mass from the surrounding cloud to collapse under the force of its own gravity to form a pressure-supported core. The nascent protostar continues to pull in mass, and the infalling material spirals around the center to create an accretion disk.

The protostar within L1527 is only 100,000 years old, so it doesn’t generate its own energy from nuclear fusion that converts hydrogen to helium like a full-fledged star. Rather, the energy comes from the radiation released by shock waves on the surface of the protostar and its accretion disk. Right now, it’s actually a spherical puffy lump of gas between 20 and 40 percent of our sun’s mass. As the protostar continues to gain mass and compress further, its core will continue to heat up. Eventually it will get hot enough to trigger nuclear fusion and a star will be born.

The Webb image above shows how material ejected from L1527’s protostar has created empty cavities above and below; the glowing orange and blue areas represent the boundaries that those areas outline. (The color of the blue area is because it has less dust in it, compared to the orange areas above it, which trap more blue light in the thick dust so it can’t escape.) The accretion disk appears as a dark band. There are also filaments of molecular hydrogen in the image, the result of shocks from the protostar’s ejection material.

List image by NASA/ESA/CSA/STScI/J. DePasquale

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