{"id":388985,"date":"2026-04-20T16:38:30","date_gmt":"2026-04-20T16:38:30","guid":{"rendered":"https:\/\/www.newsbeep.com\/nz\/388985\/"},"modified":"2026-04-20T16:38:30","modified_gmt":"2026-04-20T16:38:30","slug":"star-birth-doesnt-come-from-ignition-but-from-equilibrium","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/nz\/388985\/","title":{"rendered":"Star birth doesn’t come from ignition, but from equilibrium"},"content":{"rendered":"

Wherever star-formation happens, a classic cosmic story unfolds. <\/p>\n

\"A<\/p>\n

A spiral galaxy typically consists of four main gaseous regions within the disk: diffuse atomic gas, dense molecular gas, stars and star clusters, and ionized regions of matter arising from energy injections from star-forming regions, young stars, and stellar cataclysms. JWST, along with the other PHANGS data sources, helps reveal different aspects of this life cycle, but once a galaxy\u2019s gas is gone and no new gas reservoirs fall inside, star-formation ends permanently.\n<\/p>\n

Credit<\/a>: PHANGS collaboration, Design: Daniela Leitner<\/p>\n

Initially, a massive cloud of gas contracts under its own gravity.<\/p>\n

\"Dark<\/p>\n

This amateur astronomy image of dark nebula LDN 1551 showcases the cloud of ionized gas within it: Sharpless 239. Many protostars, surrounded by dusty disks, are located inside, along with numerous Herbig-Haro objects, as the gas cloud has regions within it that have already internally fragmented and heated up, forming protostars and even early full-fledged stars in the process.\n<\/p>\n

Credit<\/a>: KK_Astro\/Kapt\u00e0s Attila<\/p>\n

Internal gas molecules radiate heat away, enabling further shrinking.<\/p>\n

\"A<\/p>\n

Within the plane of the Milky Way, dark dust lanes are omnipresent, representing dense neutral gas clouds usually found within the galaxy\u2019s spiral arms. Here, nebula NGC 6357, also known as the Lobster Nebula, shows the pink signatures of excited hydrogen, a telltale feature of new star formation, along with the blue glow of the reflected light from hot, newborn stars off of neutral matter. Although it may not be obvious to the untrained eye, these dark clouds of material hide obscured regions of new star-formation within them as the molecular gas inside radiates heat away.\n<\/p>\n

Credit<\/a>: ESO\/VVV Survey\/D. Minniti<\/p>\n

The densest areas fragment first, diminishing further in size.<\/p>\n

\"<\/p>\n

The dense cores of protostar cluster G333.23\u20130.06, as identified by ALMA, show strong evidence for large levels of multiplicity within these cores. Binary cores are common, and groups of multiple binaries, forming quaternary systems, are also quite common. Triplet and quintuplet systems are also found inside, while, for these high-mass clumps, singlet stars turn out to be quite rare. It is expected that the stars forming in nebulae all throughout the Universe, including in the Eagle Nebula, have similar clumpy, fragmented properties.\n<\/p>\n

Credit<\/a>: S. Li et al., Nature Astronomy, 2024<\/p>\n

These most-massive regions grow quickly, becoming protostellar clumps<\/a>.<\/p>\n

\"\"<\/p>\n

This animation that fades between the 1995 Hubble view, the 2014 Hubble view, and the 2022 JWST view shows off the different views of stars, dust, knotted gas loops and outflows, and the presence of protostars. The variety of features at the top of this pillar, the 2nd one in the Pillars of Creation, is particularly notable.\n<\/p>\n

(Credits<\/a>: NASA, ESA, CSA, STScI; the Hubble Heritage Team; J. Hester and P. Scowen; animation by E. Siegel)<\/p>\n

As protostellar growth continues, gravitational potential energy converts into heat.<\/p>\n

\"yellowballs<\/p>\n

Three separate regions illustrate various stages of a newly forming star\u2019s life, which are totally obscured in the optical and can only be seen in the infrared. At left, a protostar emits radiation that\u2019s shrouded in light-blocking dust. In the center, a \u2018yellowball\u2019 occurs after the start of nuclear fusion, but still cannot be seen in the optical due to all the surrounding matter. At right, a more evolved star, with significant fusion output, has begun to blow an ionized bubble in the surrounding region. For high-mass stars, we now know that forming a singlet system, as opposed to a multi-star system, is a relative rarity.\n<\/p>\n

Credit<\/a>: NASA\/JPL-Caltech<\/p>\n

Powered by gravity, these protostars shine<\/a>: long before fusion initiates.<\/p>\n

\"\"<\/p>\n

Located roughly 58,000 light-years from the galactic center, Digel cloud 2s, highlighted here, is found in the extreme outer galaxy of the Milky Way. The main cluster, glittering brilliantly, exhibits at least five independent protostellar jets, as highlighted by the white arrows.\n<\/p>\n

Credit<\/a>: NASA, ESA, CSA, STScI, M. Ressler (NASA-JPL)<\/p>\n

As their interior temperatures rise, proton-deuterium fusion<\/a> begins.<\/p>\n

\"\"<\/p>\n

Gliese 229 is a red dwarf star, and is orbited by Gliese 229b, a brown dwarf, that underwent deuterium fusion only, never progressing to fusing protons with other protons. Although Gliese 229b is about 20 times the mass of Jupiter, it\u2019s only about 47% of Jupiter\u2019s radius: smaller despite being more massive.\n<\/p>\n

Credit<\/a>: S. Kulkarni (Caltech), D. Golimowski (JHU) and NASA\/ESA<\/p>\n

Below 0.075 solar masses, few additional fusion reactions occur: yielding brown dwarfs.<\/p>\n

\"Sun<\/p>\n

Brown dwarfs, between about 0.013-0.080 solar masses, will fuse protons+deuterons or deuterons+deuterons into helium-3 or tritium, remaining at the same approximate size as Jupiter but achieving much greater masses. Red dwarfs are only slightly larger but do initiate proton-proton fusion, but even the Sun-like star shown here is not shown to scale here; it would have about 7 times the diameter of a low-mass star. Stars can be up to nearly 2000 times the diameter of our Sun within this Universe.\n<\/p>\n

Credit<\/a>: NASA\/JPL-Caltech\/UCB<\/p>\n

At higher masses \u2014 yielding higher core temperatures \u2014 proton-dominated fusion reactions ensue.<\/p>\n

\"proton<\/p>\n

The most straightforward and lowest-energy version of the proton-proton chain, which produces helium-4 from initial hydrogen fuel. Note that only the fusion of deuterium and a proton produces helium from hydrogen; all other reactions either produce hydrogen or make helium from other isotopes of helium. This reaction set occurs in the interiors of all young, hydrogen-rich stars, regardless of mass.\n<\/p>\n

Credit<\/a>: Sarang\/Wikimedia Commons<\/p>\n

Beyond a few million K, fusion through the proton-proton chain<\/a> initiates.<\/p>\n

\"\"<\/p>\n

The evolution of a solar-mass star on the Hertzsprung-Russell (color-magnitude) diagram from its pre-main-sequence (protostellar) phase to the end of fusion and its eventual transformation into a white dwarf. Every star of every mass will follow a different curve, but the Sun is only a star once it reaches the main sequence, and ceases to be a star once helium burning (in both the core and in all shells) is completed. Stars on the upper-left of the diagram (on the main sequence) are more massive, hotter, and more luminous than our Sun, but are also the shortest-lived.\n<\/p>\n

Credit<\/a>: szczureq\/Wikimedia Commons<\/p>\n

However, initiating hydrogen burning alone doesn\u2019t signify stellar \u201cbirth.\u201d<\/p>\n

\"Hertzsprung-Russell<\/p>\n

From a contracting clump within a cloud of gas, protostars form as gravitational potential energy gets converted into thermal (heat) energy. Initially, protostars are cooler but more luminous than the stars that they will give rise to, and contract and heat up (but become smaller, with less surface area to radiate energy through) as they evolve. When they reach the curve entitled \u201czero age main sequence,\u201d that corresponds to the official \u201cbirth\u201d of the star, with the pathways of stars of different masses (relative to 1 solar mass) indicated at various points along the curve.\n<\/p>\n

Credit<\/a>: Lithopsian\/Wikimedia Commons<\/p>\n

For \u201cstar birth,\u201d the rate of fusion must balance the star\u2019s luminosity: its total power output.<\/p>\n

\"Comparison<\/p>\n

This illustration shows a size and color comparison of four different main sequence stars: the red dwarf Proxima Centauri (with no CNO reactions inside), the Sun (where only 1% of its fusion energy comes from the CNO cycle), Sirius A (where the CNO cycle outputs more energy than the proton-proton chain), and blue giant Spica (where the proton-proton chain\u2019s energy is negligible compared to the CNO cycle).\n<\/p>\n

Credit<\/a>: Daniel William Wilson\/Wikimedia Commons<\/p>\n

For more massive stars, the proton-proton chain won\u2019t generate sufficient energy; the Carbon-Nitrogen-Oxygen (CNO) cycle<\/a> must initiate.<\/p>\n

\"\"<\/p>\n

This illustration of the lowest-energy component of the CNO cycle, which is the most common mechanism by which it occurs in the Sun, details how hydrogen fuses into helium as a result of chain reactions involving carbon, nitrogen, and oxygen. In stars with more than 130% the mass of the Sun, this, rather than the proton-proton chain, dominates as far as nuclear fusion is concerned.\n<\/p>\n

Credit<\/a>: Borb\/Wikimedia Commons<\/p>\n

Such massive stars contract most quickly: a 20 solar mass star is \u201cborn\u201d after ~30,000 years.<\/p>\n

\"Hertzsprung-Russell<\/p>\n

Stars of lower masses don\u2019t merely live longer by spending more time burning through their fuel at lower rates on the main sequence, but take longer to initially form. Whereas a star born with roughly 20 times the Sun\u2019s mass will leave the protostellar phase after only tens of thousands of years, a star born with a mass similar to the Sun\u2019s will take tens of millions of years before it evolves from the protostellar phase to the main sequence.\n<\/p>\n

Credit<\/a>: Quizlet, Inc.<\/p>\n

Sun-like stars require more time: ~50 million years.<\/p>\n

\"Hertzsprung-Russell<\/p>\n

This color-magnitude (or Hertzsprung-Russell) diagram shows a \u201csnapshot\u201d of color vs. magnitude of a wide variety of stars. When stars, which begin as larger, cooler protostars, gravitationally contract and heat up so that they finally emit enough energy through nuclear fusion in their cores to equal the star\u2019s total energy output, they begin life at the bottom of the main sequence (vertically) for whatever their color is. This event marks the \u201cbirth\u201d of the star, not the ignition of fusion for the first time, which occurs long before: when temperatures merely reach approximately 1 million K in the protostar\u2019s core. Over a star\u2019s hydrogen-burning lifetime, it migrates upward, becoming brighter but remaining at approximately the same color\/temperature, before running out of hydrogen in their cores and evolving first into subgiants, and then into red giants or supergiants, where they then head into the final stages of their lives and approach their stellar demises.\n<\/p>\n

Credit<\/a>: Richard Powell\/Wikimedia Commons<\/p>\n

Only after reaching ZAMS \u2014 the zero-age main sequence<\/a> \u2014 are new stars officially \u201cborn.\u201d<\/p>\n

\"A<\/p>\n

This close-up view of the central portion of the protoplanetary system IRAS 04302+2247 showcases the motion of gaseous material away from the central protostar, while accreting material from within the disk is particularly dust-rich, obscuring even JWST\u2019s views of the central protostar. Even though nuclear fusion is occurring inside, the fact that some significant percentage of the central object\u2019s energy still comes from gravitational contraction keeps it on the \u201cprotostar\u201d side of the dividing line between a protostar and a full-fledged star.<\/p>\n

Credit<\/a>: ESA\/Webb, NASA & CSA, M. Villenave et al.<\/p>\n

Energy balance and growth cessation, not ignition, dictates stellar birth.<\/p>\n

\"Colorful<\/p>\n

This extremely young star cluster began forming stars only within the last 3 million years, making it one of the youngest star clusters known in existence. The orange color, to JWST\u2019s eyes, represents gas that glows with heat in the infrared, powered by outflows from young, massive Herbig-Haro objects. The most massive objects within this nebula have already become stars; the least massive ones are still in the protostellar phase, and may remain there for millions or even tens of millions of years to come.\n<\/p>\n

Credit<\/a>: ESA\/Webb, NASA & CSA, A. Scholz, K. Muzic, A. Langeveld, R. Jayawardhana<\/p>\n

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.<\/p>\n","protected":false},"excerpt":{"rendered":"Wherever star-formation happens, a classic cosmic story unfolds. A spiral galaxy typically consists of four main gaseous regions…\n","protected":false},"author":2,"featured_media":388986,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[111,139,69,147,392],"class_list":{"0":"post-388985","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-space","8":"tag-new-zealand","9":"tag-newzealand","10":"tag-nz","11":"tag-science","12":"tag-space"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/388985","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=388985"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/388985\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/388986"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=388985"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=388985"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=388985"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}