From April 2026 issue
One of the finest examples of a newborn emerging from the birth shroud, this cluster within the Lobster Nebula caught JWST’s infrared eye.
The young cluster Pismis 24 is located in the center of the Lobster Nebula (NGC 6357) in Scorpius. The brightest stars in our galaxy are among the hottest and most massive stars. Thousands of background stars add depth to this JWST infrared image. Credit: NASA, ESA, CSA, and STScI, A. Pagan (STScI)
If you look at a picture of a spiral galaxy head-on, you’ll see spiral arms filled with glowing gas clouds, glowing star clusters, and lanes of opaque dust spiraling slowly away from the galaxy’s core. An image of the spiral on the side gives a completely different picture. The gas, dust and stars now occupy a thin disk that shows just a hint of the gorgeous detail seen in their face-to-face cousins.
The same structures define the spiral galaxy we call home. At first glance the galaxy may appear amorphous, but that’s only because we see it from the inside. The big picture shows that most of the young star clusters and the emission nebulae that give rise to them reside in a narrow band that matches our galaxy’s equator.
a cosmic crustacean
One of the finest examples of a nascent cluster emerging from the shroud of its birth lies less than 1° from the galaxy’s equator in the constellation of Scorpius. The Lobster Nebula (NGC 6357) spans about 300 light-years and contains enough raw material to form thousands of stars. Many of its first-generation stars reside in the giant open cluster Pismis 24 at the center of the nebula.
The James Webb Space Telescope (JWST) recently captured this bright cluster in spectacular detail. Astronomers targeted Pismis 24 because it is located just 5,500 light years from Earth, a stone’s throw away in the context of the Milky Way and thus a prime location for studying massive stars and their effects on their environment.
JWST’s infrared eye penetrates most of the gas and dust that still shrouds the cluster. The light blue haze that permeates the image shows hydrogen gas ionized by the hottest and most massive stars, while dust particles glow orange and cooler, denser molecular hydrogen appears dark red.
Astronomers once thought that the cluster’s brightest star, Pismis 24-1 (seen in the center of the image), might be the most massive star in our galaxy. Its height was estimated to be up to 300 solar masses, which would put it close to the theoretical limit for the mass of a star in today’s universe. But recent observations suggest that it is a binary system consisting of stars between “only” 74 and 66 solar masses. At least half a dozen other stars in Pismis 24 join these stellar giants in spectral class O, the hottest class of normal stars.
The surface temperatures of these monsters reach about eight times that of the Sun, so the radiation they emit is energetic ultraviolet light. This ionizes the hydrogen dispersed in the Lobster Nebula and causes it to glow with the distinctive red color visible in visible-light images.
a sculptural breeze
These high-mass stars also produce fierce stellar winds, which clear away most of the surrounding gas and dust and create the cavity that allows us to see Pismis 24. The densest regions of gas and dust can resist attack for some time, forming colorful towers reminiscent of the famous “Pillars of Creation” seen in the Eagle Nebula.
The tallest tower is visible slightly below center and points directly upward toward Pismis 24-1. The tip of the summit measures 0.14 light-years, meaning more than 100 solar systems (outside Neptune’s orbit) could span across its width. But don’t expect to see many planetary systems growing in this region. Astronomers estimate that Pismis 24 has a lower frequency of protoplanetary disks than similar clusters, perhaps due to its exceptionally strong wind and radiation environment.
