Жэймс Вэбб сансрын дуран авай ашиглан хийсэн шинэ судалгаагаар эртний орчлон ертөнцөд галактикууд нэгдэж, сансрын дахин ионжилтыг эхлүүлсэн байж болзошгүй тохиолдлыг илрүүлжээ.
Жэймс Вэбб сансрын дуран авайгаар (JWST) хийсэн JADES судалгааны хүрээнд одон орон судлаачид Их тэсрэлтээс хойш 500 сая хүрэхгүй жилийн дараах үед хамаарах галактикийн нягт бөөгнөрлийг илрүүлжээ. Харвардын Смитсоны нэрэмжит Астрофизикийн төвийн судлаач Зихао Ву болон түүний баг 18 галактикийг багтаасан энэхүү бүлэг нь тухайн орон зайн дундаж үзүүлэлтээс дөрөв дахин их нягттай болохыг тогтоосон байна. Энэхүү нээлт нь эртний орчлон ертөнцийн харанхуй, тунгалаг бус төлөвөөс гэрэлтэй төлөв рүү шилжих үйл явц буюу дахин ионжилтын шалтгааныг тайлбарлахад чухал ач холбогдолтой юм.
Судлаачид уг бүс нутгаас устөрөгчийн ялгаруулдаг Лиман-альфа спектрийн шугамыг илрүүлсэн нь онцгой ач холбогдолтой байна. Лиман-альфа фотонууд төвийг сахисан устөрөгчид амархан сарнидаг тул дахин ионжилтын өмнөх үед тэдгээрийг ажиглах нь бараг боломжгүй гэж үздэг. Гэвч тус бүс нутагт ажиглагдсан Лиман-альфа цацрагийн орон зайн хувьсал нь 6 орчим cMpc радиустай ионжуулагч хөөсөн бүрхүүл үүссэнийг баталж байна.
Энэхүү хөөсөн бүрхүүл нь эртний галактикуудын бөөгнөрөл хүрээлэн буй орчныхоо төвийг сахисан устөрөгчийг ионжуулж, гэрэл нэвтрэх нүх сүвийг анхлан нээж байсны нотолгоо байж болох юм. Хэдийгээр эдгээр дүгнэлт нь одоогоор спектроскопийн судалгаанд үндэслэсэн урьдчилсан таамаглал төдий байгаа ч ирээдүйн ажиглалтууд үүнийг батлах боломжтой. Судлаачид JWST болон ALMA дуран авайг ашиглан тус бүс нутгийн гурван хэмжээст бүтцийг нарийвчлан зураглаж, дахин ионжилт дахь үүргийг нь тодорхойлохоор төлөвлөж байна.
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When the JWST’s first science results started rolling in, it was a triumph for scientific vision and persistence. For years, the fate of the powerful space telescope was uncertain. It went way over budget, and for 25 years, troubling conversations accompanied its ongoing development. Several times, it seemed like it would be cancelled, and in 2011, congress came close to ending the program.
So when it was finally launched on December 25th, 2021, there was a collective sigh of relief in the astronomy community. As it began observations, astronomers, cosmologists, exoplanet scientists, and astrophysicists around the world anticipated the telescope’s findings.
The telescope didn’t disappoint. The JWST found surprisingly bright, well-developed galaxies only several hundred million years after the Big Bang, clashing with our scientific understanding at the time. Since its initial observations, the JWST has continued to stun us with its early Universe findings.
One of the JWST’s first and most important surveys was JADES, the JWST Advanced Deep Extragalactic Survey. JADES is responsible for many of the telescope’s surprising observations of the young Universe.
The shock at the JWST’s findings has subsided somewhat, and now astronomers are examining these findings more deeply to see what they can learn. In new research in The Astrophysical Journal based on JADES, researchers found a “galaxy overdensity candidate” that could help explain the Universe’s reionization. Reionization is when the first stars and galaxies formed and illuminated their surroundings, reionizing hydrogen atoms in the primordial Universe. Prior to this, the Universe was opaque and dark. After this, photons were free to travel and the cosmos lit up.
The research is titled “JADES: A Prominent Galaxy Overdensity Candidate within the First 500 Myr,” and the lead author is Zihao Wu. Wu is from the Center for Astrophysics ∣ Harvard & Smithsonian.
“We report a galaxy overdensity candidate at z ≈ 10.5 in the JWST Advanced Deep Extragalactic Survey,” the authors write. It contains 18 galaxies in a co-moving group, which is a very dense arrangement. “The galaxy number density is 4 times higher than the field expectation, accounting for one-third of comparably bright galaxies and nearly 50% of the total star formation rate (SFR)” in a specific field and redshift in the GOODS-S field.
This figure from the research shows the distribution of galaxies in the field. The overdensity is on the western side of the GOODS-S field, on the right in this image. It’s about 4 times as dense as the field average. Image Credit: Wu et al. 2026. ApJ
More of the galaxies in this overdensity have close companions and substructures than in the field at large, and the authors say that’s evidence of interactions. The stellar masses of these galaxies, and their star formation rates, are a little higher compared to the galaxies in the field, but are still consistent with high-redshift expectations. So while they’re interacting more than field galaxies, they don’t seem to be experiencing rapid star formation.
But what they appear to be doing is blowing large bubbles.
The researchers found Lyman-alpha transmissions in the region. Lyman-alpha is a specific UV spectral line that hydrogen emits when an electron loses energy. It’s normal to find Lyman-alpha radiation in star-forming galaxies because young stars pump out a lot of it. But Lyman-alpha photons have a very interesting property: they’re easily scattered by neutral hydrogen.
Astronomers don’t expect to see my Lyman-alpha radiation in the early Universe because it essentially bounces off of neutral hydrogen in the interstellar medium. So it would either be blocked, or at least highly attenuated. Detecting Lyman-alpha before reionization is thought to be nearly impossible.
What makes this detection particularly interesting is that it’s also spatially variable. “We find tentative evidence for spatial variation in Lyα transmission from the photometric data, consistent with the formation of an ionizing bubble with radius ∼6 cMpc,” the authors write.
The spatial variation in the Lyman-alpha radiation has a pattern. “It is elevated near the center of the overdensity and decreases toward the outskirts,” the researchers explain. “This behavior is consistent with enhanced Lyα transmission in the core and reduced transmission in the outskirts.”
That’s evidence that the Lyman-alpha radiation is visible as it reaches the boundary of a bubble of reionization.
What the researchers found could be evidence of the first stages of cosmic reionization. In this scenario, galaxy overdensities like this one were responsible for some of the initial reionization, carving bubbles in the neutral hydrogen that dominated the early Universe. These galaxy overdensities could be responsible for kicking off the reionization.
“If confirmed, the spatial variation of Lyα transmission would mark the earliest ionized bubble produced by a galaxy overdensity known so far,” the authors write. “It provides a rare laboratory to study the structure of ionizing bubbles.”
The authors explain that these aren’t firm conclusions, because they’re based solely on spectroscopy. In the future, the researchers say they’ll observe the overdensity again, with the JWST and with ALMA, targeting hydrogen-alpha and doubly-ionized oxygen.
“Together, these observations will map the three-dimensional structure of the overdensity and provide a direct test of its role in cosmic reionization within the first 500 Myr of the Universe,” the authors conclude.
