Jump to content

Evidence for the First Generation of Stars

Avi Loeb Medium
 Share

Recommended Posts

Avi Loeb Medium Newbie

Avi Loeb Medium

Posted
Posted
1*Oy7aCWasS7QM8lEbdgQAlQ.jpeg
Schematic illustration of the progenitor of a supermassive black hole in the form of a supermassive star. After the accretion of gas into the supermassive star ends, the star contracts, ignites hydrogen burning, and re-expands into a late phase of instability. Pulsation-driven mass loss then proceeds through discrete ejection episodes that remove weakly-bound envelope material. Earlier shells expand to large radii, whereas the final pre-collapse ejection remains compact and dense, setting the immediate circumstellar environment which explain Webb telescope data on the observed population of `little red dots’. The ejecta carries a characteristic abundance pattern which is consistent with spectroscopic observations by the Webb telescope. The supermassive star then continues toward collapse through a General Relativistic instability owing to Einstein’s gravity and ultimately ends as a heavy black-hole seed for a quasar. (Image credit: Devesh Nandal et al. 2026)

Two new papers today provide evidence for the first generation of stars, made solely from the primordial gas of hydrogen and helium left from the Big Bang. Middle-aged stars like the Sun recycle material that was already processed through nuclear fusion in the interiors of stars. However, the primordial material that made first stars had no heavy elements. As a result, it did not cool efficiently and condensed into massive stars. The first stars with masses exceeding ten solar masses, had a surface temperature of up to 10⁵ degrees and acted as efficient factories of ultraviolet radiation.

This was a theoretical prediction that I derived with my students and postdocs at Harvard University thirty years ago. The earliest publications included a paper, accessible here, that I co-authored with my former postdoc Volker Bromm and Rolf Kudritzki in 2001. Our calculations demonstrated that the ultraviolet radiation from the early stars would break hydrogen and helium atoms in their vicinity, and result in the emission of a distinct spectral line from a singly-charged helium ion at a wavelength of 0.1640 micrometers, labeled He II λ1640. The theoretical predictions from my research were summarized in two textbooks that I published a decade later, titled: “How Did the First Stars and Galaxies Form?” and “The First Galaxies in the Universe”.

Recent spectroscopic observations by the Webb Telescope detected the emission of a strong He II λ1640 spectral line in the vicinity of an early galaxy, labeled GN-z11, at a cosmological redshift of z=10.6. This galaxy existed 13.4 billion years ago, just 400 million years after the Big-Bang. No heavy elements were identified in its spectrum. The properties of the spectral-line source, labeled Hebe, can be explained by a cluster of first-generation stars. A new paper, posted here, studies an alternative source for the ultraviolet radiation in the form of an accreting supermassive black hole. The authors show that a star cluster with a total mass of 10⁵ solar masses can explain the data more naturally. Such a cluster of first generation of stars constitutes the limit of what is expected in theoretical calculations dating back to my work with Bromm and Kudritzki.

My interest in this topic started as early as in 1994, shortly after my arrival as junior faculty at Harvard, when I published a paper — accessible here — with Fred Rasio, suggesting that the progenitors of the first supermassive black holes at the centers of galaxies are supermassive stars. Our model suggested that as a result of inefficient cooling, a clump of primordial gas would generically condense at the center of the first galaxies without fragmenting into low-mass stars. The collapse of this primordial cloud would result in a supermassive star that lives for about a million years and eventually collapses to a seed of a quasar black hole. The early population of quasars are known to be black holes which accrete gas at the center of galaxies. Bright quasars peaked in abundance during the first few billion years after the Big-Bang.

Other observations by the Webb telescope reveal the existence of a population of `little red dots’, compact reddish galactic cores which existed during the era of quasar formation. Could these `little red dots’ be the seeds of quasar black holes? This was indeed the suggestion we made in a paper that I recently published in collaboration with Fabio Pacucci, accessible here.

But there is another new paper that I co-authored today, available here, which was led by my postdoc Devesh Nandal. The paper explains that the spectral properties of `little red dots’ requires dense gas close to the source, yet the physical origin of that cocoon-like structure remains unclear. Our paper shows that late-time episodic mass-loss from supermassive stars leads to the required dense gas cocoons.

After the accretion of gas into the supermassive star ends, the star contracts, ignites hydrogen burning, and re-expands into a late phase of instability. Pulsation-driven mass loss then proceeds through discrete ejection episodes that the remove weakly-bound envelope material. The earlier shells expand to large radii, whereas the final ejection remains compact and dense, setting the immediate circumstellar environment relevant to the `little red dot’ phase. The ejecta carries a characteristic abundance pattern which is consistent with spectroscopic data from the Webb telescope. The supermassive star then continues toward a General Relativistic instability and ultimately collapses into a heavy black-hole seed owing to Einstein’s gravity.

Our paper examines five models with different abundances of heavy elements, all having progenitor masses of order 10⁵ solar masses. We followed the evolution of these supermassive stars after they stop accreting gas with radial pulsations calculations and general relativistic stability diagnostics. Mass loss during the final stages of evolution occurs not as a steady wind, but through discrete strange-mode ejection episodes. In the nearly pristine gas case, there were four late episodes that last 41 to 282 years and eject 10 to 348 solar masses each, for a total loss of 480 to 1,000 solar masses. The final episode alone contributes 73% of the mass-loss, and leaves behind a compact, opaque shell extending out to a light-year that reproduces the dense gas cocoons in `little red dots’.

The final ejecta is dominated by hydrogen and helium but is also rich in nitrogen, as observed in `little red dots’. A supermassive star reaches the General Relativistic instability at an age of about a million years and eventually collapses within a few hours, retaining almost all of its mass.

All in all, these calculations demonstrate that supermassive stars provide a physically motivated origin for the compact cocoon-like structure associated with `little red dots’, while remaining the natural progenitors of massive black hole seeds for quasars.

It took 32 years to confirm my early conjecture with Fred Rasio on this subject, but the journey was definitely worthwhile. I regard 32 years as a discounted wait period. After all, according to the Old Testament, the Israelites spent 40 years wandering in the desert before reaching the promised land.

ABOUT THE AUTHOR

1*LE3Xlzc3hNG5VDAGlDP8KQ.jpeg
(Image Credit: Chris Michel, National Academy of Sciences, 2023)

Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, former director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics (2005–2026), and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.

Professional website:

https://lweb.cfa.harvard.edu/~loeb/

Social media:

https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb

https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb

stat?event=post.clientViewed&referrerSou

View the full article

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
 Share
Go to topic listing

  • Similar Topics

    • SpaceObserver
      The First Potential Detection Of A Dark Matter Particle
      By SpaceObserver
      Recent discussions around dark matter have been reignited with the announcement of the first potential detection of a dark matter particle. This event not only captures the imagination but also stands as a pivotal moment in our ongoing quest to understand the universe's unseen components.
      In the video, John Michael Godier explores the findings related to the LUX-ZEPLIN (LZ) experiment, which aims to observe dark matter interactions. The study, "Search for dark matter particle interactions in an extended nuclear recoil energy window with the LUX-ZEPLIN (LZ) experiment" by Akerib et al., outlines the experimental framework and the significance of these potential detections. The implications of this research could help answer longstanding questions about the composition of our universe, which is thought to be made up of approximately 27% dark matter, yet remains largely elusive.
      What's particularly intriguing about this development is how it compares to previous dark matter research attempts. For instance, earlier experiments such as the Large Underground Xenon (LUX) project laid the groundwork for understanding dark matter interactions. However, the LZ experiment takes a significant leap forward by expanding the energy window for detection, potentially increasing the chances of identifying a dark matter particle.
      Nevertheless, the evidence is still tentative. The term 'potential detection' implies that while there may be signals indicative of dark matter interactions, they are not yet confirmed. The scientific community often approaches such findings with a healthy dose of skepticism until further verification is achieved. The results need to be reproducible and peer-reviewed to gain wider acceptance.
      Additionally, it's important to consider the limitations of the current research. While the LZ experiment's methodology is robust, the detection of dark matter particles depends heavily on factors such as background noise and the sensitivity of the detection equipment. The physicists involved must contend with numerous variables that could obscure or mimic the signals they are trying to capture.
      As we await further updates from the LZ collaboration, it's worth pondering how this finding might influence our understanding of cosmology. If confirmed, the detection of dark matter could lead to revolutionary changes in the theoretical frameworks we use to describe the universe. How might it impact future research directions, or even the search for new physics beyond the Standard Model?
      Given the complexities and uncertainties surrounding dark matter, one focused question for discussion is: What are the potential ramifications for cosmology if the existence of dark matter particles is definitively confirmed?
    • DisclosureWatch
      UFO Whistleblowers Claim Evidence Exists Beyond Public Knowledge
      By DisclosureWatch
      In a recent episode of Reality Check, Ross Coulthart discusses claims from whistleblowers who allege that significant evidence related to UFOs and UAPs has yet to be made public. He mentions that these whistleblowers come forth with information about crash-retrieval and reverse-engineering programs. These claims raise questions about what information is truly accessible and what remains locked away due to government regulations.
      Coulthart specifically references Dr. Eric Davis, who claims to have seen classified records and photographs related to UAPs, including those he describes as possibly linked to nonhuman bodies. This assertion, if true, could represent a major shift in our understanding of UAPs and their implications. However, it's essential to approach these claims with a critical eye due to the lack of verifiable evidence in the public domain.
      The video also highlights the ongoing release of UAP files from the Trump administration, which aims to increase transparency regarding military encounters with unidentified aerial phenomena. While some files have surfaced, many in the community are left wondering what remains classified and why. The push for more comprehensive disclosure is growing, yet the bureaucratic obstacles seem to persist.
      What stands out is Coulthart's emphasis on the need for clarity surrounding the government's stance on UAPs. He seems to suggest that current policies hinder the full disclosure of important information that could inform both public understanding and scientific inquiry. This leaves many skeptics questioning what the real motives behind these restrictions might be.
      One critical point is how the presence of whistleblowers shapes the dialogue around UFOs. Their accounts, while compelling, often lack the necessary evidence to substantiate their claims. This raises the question of how much weight should be given to personal testimonies when discussing government transparency and accountability in relation to UAPs.
      As this conversation unfolds, it prompts us to consider the balance between national security and the public's right to know. Are there valid reasons for keeping certain information classified? Or does this simply contribute to a culture of secrecy that fuels speculation and mistrust? What's your take on the validity of these whistleblower claims, and how do you think they should influence the ongoing discourse about UFOs and government disclosure?
    • SpaceObserver
      The First Potential Detection Of A Dark Matter Particle With Prof. Matthew Szydagis
      By SpaceObserver
      In a recent video, Prof. Matthew Szydagis discusses what might be the first detection of a dark matter particle, which is a significant point of interest in astrophysics. Dark matter is thought to make up nearly 27% of the universe, yet it remains elusive and undetected directly. This potential finding could be a breakthrough in understanding the fundamental structure of our universe.
      The video outlines the methods used in the detection process and how this finding was reached. Szydagis highlights the role of advanced detectors and collaborations among various research institutions. These efforts, combined with sophisticated modeling, make it possible to interpret the data collected, though the physical implications remain largely theoretical at this stage. The nature of dark matter particles continues to challenge scientists, who have yet to pinpoint their exact characteristics or behaviors.
      Importantly, this detection is not definitive; the scientific community is well aware of the need for further validation. Skepticism in the field is healthy, especially when dealing with concepts as abstract as dark matter. The implications of this detection could inform future research directions, but it will require rigorous testing and verification. The reliance on indirect evidence has always been a point of contention among physicists, and while the findings are intriguing, they must be approached with caution.
      Additionally, the video touches upon the historical context of dark matter research. From the early 20th century studies of galaxy rotation curves to the recent advancements in particle physics, the journey to understand dark matter has been long and fraught with challenges. This recent claim is a testament to the evolving nature of scientific inquiry, where each step forward is met with both excitement and skepticism.
      As we explore these findings, it’s also worth considering how this potential detection might intersect with other areas of astronomy and cosmology, particularly in the quest to understand our universe's composition. Could this lead to new insights in exoplanet research or influence future missions, such as those involving the James Webb Space Telescope (JWST)?
      Dark matter remains one of the most intriguing mysteries of our cosmos. As scientists push the boundaries of our understanding, the question remains: what would it take to definitively confirm or refute the existence of dark matter particles? This ongoing investigation continues to ignite curiosity within the scientific community and beyond.
    • SpaceObserver
      Is This The First Confirmed Exomoon Orbiting A Brown Dwarf?
      By SpaceObserver
      Astronomers have been on the hunt for exomoons for decades, but concrete evidence of these celestial bodies has remained elusive. Recently, a team led by PhD student Kevin Hoy from Universidad Diego Portales suggested they may have detected something intriguing: a candidate satellite orbiting a brown dwarf, CD-35 2722 B. However, there's a catch—Hoy is cautious about calling it an exomoon just yet.
      In a recent discussion on SETI Live, Hoy emphasized that while they're confident the object exists, its classification remains uncertain. The term 'satellite' is currently used to describe it, as it orbits a brown dwarf rather than a typical planet. This is significant because brown dwarfs sit in a unique mass range, bridging the gap between the largest planets and the smallest stars. They don't sustain hydrogen fusion like stars do, but they are more massive than typical planets.
      The candidate object has an eccentric orbit, which complicates its formation story. Traditionally, objects in a disk formation scenario would have more circular orbits. The current estimates suggest its eccentricity is around 0.4, while the brown dwarf itself has an eccentricity of approximately 0.8. This raises questions about how such a system could form, as there isn't a straightforward explanation provided by current models. Hoy mentioned gravitational instability as one potential formation pathway, where a massive disk might fragment under its own gravity, but this remains speculative.
      To detect this potential moon-like object, the team employed radial velocity measurements using the CRIRES+ instrument on the Very Large Telescope (VLT). This method looks for the slight wobbles of the brown dwarf caused by the gravitational pull of its companion. It's a technique similar to how planets are discovered around stars, but in this case, the target is a brown dwarf instead.
      The discovery, if confirmed, could reshape our understanding of exomoon formation and the dynamics of such systems. It also highlights the challenges in classifying celestial objects that defy simple definitions. As it stands, Hoy's team has observed something noteworthy, but the uncertainty surrounding its classification leaves us with more questions than answers.
      With this ambiguity in mind, it’s fascinating to consider: how do we define a moon in contexts like these, especially when the object orbits something that isn't a conventional planet? What criteria should we use to classify such objects, and how might this influence our search for life beyond our solar system? These questions underscore the complexities of astrobiology and the ongoing exploration of our universe.
    • DeepSkyExplorer
      NASA's Pandora Mission Observes Exoplanet Atmospheres And Host Stars
      By DeepSkyExplorer
      Pandora, NASA's latest mission, is diving into the study of exoplanets and their host stars, aiming to clarify how a star's light affects our understanding of exoplanet atmospheres. This is particularly interesting because we’ve had limited insight into the atmospheric make-up of these distant worlds until now. The mission plans to analyze at least 20 exoplanets, specifically looking for key elements like water, clouds, and hazes.
      This mission stands out as it utilizes a novel all-aluminum telescope with an 18-inch diameter, a unique feature that allows for simultaneous observations in both visible and infrared light. This approach is crucial because it enables Pandora to gather data over extended periods, which is something flagship missions like the James Webb Space Telescope (JWST) can't always do due to their focus on brief transits.
      During these transits, when an exoplanet passes in front of its host star, some of the starlight filters through the planet's atmosphere. This interaction leaves chemical fingerprints in the light that we can analyze. Yet, there’s a complication: the light we receive also includes contributions from the star itself, which isn't uniform in brightness. As noted by Benjamin Rackham from MIT, this means we have to be careful in interpreting the data, as areas of the star can be hotter or cooler, affecting our measurements.
      Elisa Quintana, the principal investigator of the mission, pointed out that this study could help us close a significant knowledge gap about exoplanets by giving us a clearer picture of how host stars influence the atmospheres of these planets. It's fascinating to think about how much we still don’t know, especially considering how star variability can throw our measurements off.
      I can’t help but think about how this mission might change what we know about potential habitability in these exoplanets. If Pandora finds consistent signatures of water vapor among its targets, it could really shift our understanding of where life might exist beyond Earth. And with this data, future missions using JWST could have a better foundation for interpreting those complex atmospheres that Pandora is now starting to unravel.
      Another interesting aspect is how the mission's near-infrared detector is actually a spare originally developed for Webb. It’s like a second chance for that technology, and now it’s contributing to a mission designed to be faster and more cost-effective. This dual-use of technology can be a game changer in how we explore space, don’t you think?
      So, now that Pandora is officially in science mode, I’m curious about what specific findings might emerge from its observations. Given that it’s monitoring exoplanets in detail over longer periods, what do you think are the chances we’ll see groundbreaking discoveries about their atmospheres or even signs of habitability? What would you want to know if you were part of the mission team?
×
×
  • Create New...