Free Astronomy Magazine May-June 2025

32 MAY-JUNE 2025 ASTRO PUBLISHING sure, and gravity being among the most important. More specifically, as frag- ments contract under the force of gravity, their cores heat up. If a core is massive enough, it will begin to fuse hydrogen. The out- ward pressure created by that fusion counteracts gravity, stopping collapse and stabilizing the object (then known as a star). However, fragments whose cores are not compact and hot enough to burn hydro- gen continue to contract as long as they radiate away their internal heat. “The cooling of these clouds is important because if you have enough internal en- ergy, it will fight that grav- ity,” says Michael Meyer of the University of Michigan. “If the clouds cool effi- ciently, they collapse and break apart.” Fragmentation stops when a fragment becomes opaque enough to reab- sorb its own radiation, thereby stopping the cooling and preventing further collapse. Theories placed the lower limit of these frag- ments anywhere between one and ten Jupiter masses. This study signif- icantly shrinks that range as Webb’s census counted up fragments of dif- ferent masses within the nebula. “As found in many previous studies, as you go to lower masses, you actu- ally get more objects up to about ten times the mass of Jupiter. In our study with the James Webb Space Telescope, we are sensitive down to 0.5 times the mass of Jupiter, and we are finding significantly fewer and fewer things as you go below ten times the mass of Jupiter,” De Furio explained. “We find fewer five-Jupiter-mass objects than ten- formation and planetary research given their similar- ities to both stars and plan- ets. NASA’s Hubble Space Telescope has been on the hunt for these brown dwarfs for decades. Even though Hubble can’t ob- serve the brown dwarfs in the Flame Nebula to as low a mass as Webb can, it was crucial in identifying candi- dates for further study. This study is an example of how Webb took the baton— decades of Hubble data from the Orion Molecular Cloud Complex—and en- abled in-depth research. “It’s really difficult to do this work, looking at brown dwarfs down to even ten Jupiter masses, from the ground, especially in regions like this. And having existing Hubble data over the last 30 years or so allowed us to know that this is a really useful star-forming region to tar- get. We needed to have Webb to be able to study this particular science topic, ” said De Furio. “It’s a quantum leap in our ca- pabilities between understanding what was going on from Hubble. Webb is really opening an entirely new realm of possibilities, under- standing these objects,” explained astronomer Massimo Robberto of the Space Telescope Science Institute. This team is continuing to study the Flame Nebula, using Webb’s spectro- scopic tools to further characterize the different objects within its dusty cocoon. “There’s a big overlap be- tween the things that could be plan- ets and the things that are very, very low mass brown dwarfs,” Meyer stated. “And that’s our job in the next five years: to figure out which is which and why.” ! Jupiter-mass objects, and we find way fewer three-Jupiter-mass ob- jects than five-Jupiter-mass objects. We don’t really find any objects below two or three Jupiter masses, and we expect to see them if they are there, so we are hypothesizing that this could be the limit itself.” Meyer added, “Webb, for the first time, has been able to probe up to and beyond that limit. If that limit is real, there really shouldn’t be any one-Jupiter-mass objects free-float- ing out in our Milky Way galaxy, un- less they were formed as planets and then ejected out of a planetary system.” Brown dwarfs, given the difficulty of finding them, have a wealth of infor- mation to provide, particularly in star T his video alternates between a Hubble Space Telescope and a James Webb Space Telescope observation of the Flame Nebula, a nearby star-forming nebula less than 1 million years old. In this comparison, three low-mass objects are highlighted. In Hubble’s observation, the low-mass objects are hidden by the region’s dense dust and gas. However, the objects are brought out in the Webb observation due to Webb’s sensitivity to faint infrared light. [NASA, ESA, CSA, Alyssa Pagan (STScI)]