Utilizing NASA’s James Webb Space Telescope, or JWST, a group of scientists, including astronomers from the University of Michigan, are approaching an answer to a pressing cosmic inquiry.

By examining the Flame Nebula, they aim to ascertain what’s the smallest astronomical body that can emerge independently from clouds of gas and dust in the universe.

The Flame Nebula, situated roughly 1,400 light-years from Earth, serves as a dynamic hub for star creation and is less than 1 million years old. Within the Flame Nebula, there exist entities so minute that their cores will never achieve hydrogen fusion like bona fide stars—these are brown dwarfs.

Frequently referred to as “failed stars,” brown dwarfs dim significantly over time and maintain much lower temperatures than stars. These characteristics complicate observations of brown dwarfs with most telescopes, making them difficult, if not impossible, to detect even at relatively short cosmological distances from the sun. However, in their youth, they remain comparably warm and luminous, thus facilitating observation despite the dense dust and gas obscuring the Flame Nebula in this instance.

JWST possesses the capability to penetrate this thick, dusty area and detect the faint infrared emissions from young brown dwarfs. The research team harnessed this ability to investigate the minimum mass threshold of brown dwarfs within the Flame Nebula.

The scientists discovered freely-floating entities that are approximately two to three times the mass of Jupiter, although they were capable of detecting objects down to 0.5 times the mass of Jupiter. The findings from this study have been approved for publication in The Astrophysical Journal Letters.

“The objective of this initiative was to investigate the essential low-mass boundary of the star and brown dwarf formation process. With Webb, we can delve into the faintest and lowest mass entities,” stated lead author Matthew De Furio.

Currently a postdoctoral fellow at the University of Texas, De Furio began analyzing JWST’s data as a graduate student at U-M. His advisor, professor and department chair Michael Meyer, also serves as a senior author for the recent study.

In fact, Meyer has been engaged with JWST now for many years, prior to its 2021 launch, aiding in the planning and development of its scientific functionalities. That effort is now benefiting a fresh wave of researchers, utilizing advanced instruments to enhance our comprehension of the cosmos.

“Everyone who has been involved with JWST for a substantial period has envisioned what the upcoming generation of astronomers would be able to achieve with it,” Meyer remarked. “These findings, produced by this capable team under Matthew De Furio’s guidance, exemplify the fulfillment of that promise.”

Smaller fragments

The low-mass threshold the team aimed for is established through a phenomenon known as fragmentation. Here, expansive molecular clouds, the birthplaces of both stars and brown dwarfs, disintegrate into smaller and smaller components, or fragments.

Fragmentation is influenced by various elements, with the interplay of temperature, thermal pressure, and gravity being some of the most critical. More specifically, as fragments compress under gravitational force, their cores increase in temperature. Should a core possess sufficient mass, hydrogen fusion will commence.

The outward force resulting from this fusion counters gravity, halting collapse and stabilizing the entity, which is then categorized as a star. Conversely, fragments lacking cores that are dense and hot enough to ignite hydrogen continue to shrink as long as they dissipate their internal heat.

“Cooling of these clouds is vital because if there is enough internal energy, it will resist gravitational forces,” Meyer stated. “When the clouds cool effectively, they undergo collapse and fragmentation.”

Fragmentation ceases when a fragment becomes dense enough to reabsorb its own emitted radiation, thus halting cooling and impeding further collapse. Theories proposed the lower limit of these fragments to lie anywhere from one to 10 Jupiter masses. This examination substantially narrows that spectrum as JWST’s inventory counted various fragments of differing masses within the nebula.

Prior investigations have indicated that there seems to be an increase in low-mass entities up to a specific point, beyond which the trend reverses. In other words, lower-mass objects become increasingly uncommon.

“Our findings indicate fewer five-Jupiter-mass entities than ten-Jupiter-mass ones, and notably fewer three-Jupiter-mass entities compared to five-Jupiter-mass entities,” De Furio remarked. “We hardly encounter any objects beneath two or three Jupiter masses, and we anticipate finding them if they exist.”

This has led the researchers to speculate they may have indeed located the lower limit they were seeking.

“Webb, for the first time, has been able to explore up to and perhaps beyond that limit,” Meyer noted. “If that limit is accurate, there shouldn’t be any one-Jupiter-mass objects freely floating in our Milky Way galaxy unless they originated as planets that were later expelled from their planetary systems.”

Advancing Hubble’s Legacy

Brown dwarfs, due to the challenges in locating them, hold a wealth of insights to offer, especially in the fields of star formation and planetary research, considering their resemblances to both stars and planets. NASA’s Hubble Space Telescope has been searching for these brown dwarfs for many years.

Although Hubble cannot detect the brown dwarfs in the Flame Nebula at the same low mass thresholds as JWST, it was instrumental in pinpointing candidates for further examination. This study exemplifies how JWST has continued the legacy of decades of Hubble data from the Orion Molecular Cloud Complex and has enabled detailed exploration.

“Conducting this research, examining brown dwarfs down to even ten Jupiter masses, is incredibly challenging from ground-based observatories, especially in regions like this. Having Hubble’s data over the last 30 years provided insights that this is a highly conducive star-forming area to target,” De Furio mentioned. “We required Webb to delve into this specific scientific area.”

Astronomer Massimo Robberto from the Space Telescope Science Institute expressed, “There’s a significant advancement in our abilities to understand what was happening from Hubble. Webb is truly unlocking an entirely new set of possibilities for comprehending these objects.”

This team continues to investigate the Flame Nebula, employing JWST’s spectroscopic instruments to further classify the various entities within its dusty veil.

“There is a substantial overlap between potential planets and very low-mass brown dwarfs,” Meyer remarked. “And that’s our mission in the upcoming five years: to discern which is which and comprehend the reasons behind them.”

Authored by Matthew Brown, Space Telescope Science Institute