Astronomy
Does coming off antidepressants really cause withdrawal symptoms?
Does coming off antidepressants really cause withdrawal symptoms?
Primordial Black Holes Can Only Explain a Fraction of Dark Matter
What is Dark Matter? That question is prominent in discussions about the nature of the Universe. There are many proposed explanations for dark matter, both within the Standard Model and outside of it.
One proposed component of dark matter is primordial black holes, created in the early Universe without a collapsing star as a progenitor.
The dark matter problem is a missing mass problem. Galaxies should not hold themselves together according to their observable mass. Their observable mass is stars, gas, dust, and a sprinkling of planets.
Some other form of mass must be present to prevent galaxies from essentially dissipating. Dark matter is a placeholder name for whatever that missing mass may be. Astronomer Fritz Zwicky first used the term in 1933 when he observed the Coma Cluster and found indications of missing mass. About 90% of the Coma Cluster is missing mass, which Zwicky called “dunkle Materie.”
This Hubble Space Telescope mosaic shows a portion of the immense Coma galaxy cluster that contains more than 1,000 galaxies and is located 300 million light-years away. The rapid motion of its galaxies was the first clue that dark matter existed. Image Credit: NASA, ESA, J. Mack (STScI) and J. Madrid (Australian Telescope National FacilityPrimordial black holes (PBHs) are one leading candidate for dark matter. In the Universe’s earliest times, pockets of dense subatomic matter may have formed naturally. Once dense enough, they could’ve collapsed directly into black holes. Unlike their astrophysical counterparts, they had no stellar progenitors.
Recent JWST observations and LIGO/Virgo results support the idea that PBHs are dark matter. Some researchers go further and say that this evidence supports the idea that dark matter is exclusively made of PBHs and has no other components.
New research suggests that some of the early PBHs would merge and that LIGO/Virgo can detect the gravitational waves from mergers. The research is “Constraints on primordial black holes from LIGO-Virgo-KAGRA O3 events.” The lead author is M. Andres-Carcasona, a PhD student at the Institute of High Energy Physics at the Barcelona Institute of Science and Technology.
An image based on a supercomputer simulation of the cosmological environment where primordial gas undergoes the direct collapse into a black hole. Credit: Aaron Smith/TACC/UT-Austin.In 2015, LIGO (Laser Interferometer Gravitational-Wave Observatory) detected its first black hole merger. At the time, researchers heralded this new window into the Universe. Until then, astronomical observations were based on electromagnetic radiation, but LIGO/Virgo changed that.
Now, Japan has joined the LIGO/Virgo collaboration with their Karga gravitational wave observatory, and the international effort is named LIGO/Virgo/Karga (LVK.) Together, the three observatories gather data on gravitational waves.
“Previous works have explored the use of GW data to find direct or indirect evidence of PBHs,” the authors write. “Specifically targeted searches of subsolar mass compact objects, which would provide a smoking gun signal of the existence of PBHs have so far been unsuccessful.”
The authors point out that within our growing body of GW data, there may be indications of PBHs that were missed by other researchers’ methods. They write that some of the component masses “… fall in regions where astrophysical models do not predict them, potentially suggesting for a PBH population,” they write.
This ESA graphic shows how we might discover primordial black holes and help solve the dark matter mystery using the JWST and LISA, the Laser Interferometer Space Antenna. Unfortunately, LISA’s launch is at least a decade away. Image Credit: ESAThe mass function of PBHs plays a large role in the formation of PBHs. Their goal is to update the mass constraints on PBHs in GW data. “One of our aims is to derive constraints which do not depend significantly on the underlying formation scenario. Thus, we consider a variety of different PBH mass functions,” they explain.
The two underlying formation scenarios they mention are astrophysical and primordial. Within the primordial category, there are different ways that PBHs can form, and they’re all tangled up with mass function. The authors explain that PBHs could explain the totality of dark matter, but only if they’re within the range of 10-16 to 10-12 solar masses.
“Lighter PBHs would be evaporating today and can constitute only a small portion of the DM,” they write.
Astrophysical BHs form binaries and can merge, sending out gravitational waves. If PBHs merge, they would also send out gravitational waves. It’s possible that some of these mergers are behind some of the GW data detected by LIGO/Virgo/Karga in its third observational run. The researchers present their results in terms of a pessimistic case and an optimistic case. The pessimistic case says that all GW observations are from Astrophysical Black Hole (ABH) mergers, while the optimistic case suggests that some are from PBH mergers.
Their research and its results involve an awfully large number of complicated physical terms and relationships. But the main question is whether PBHs can comprise dark matter, either partly or wholly. In that context, what do the results boil down to?
This artist’s illustration shows small black holes in the accretion disk of a supermassive black hole. In early 2024, a team of researchers found evidence of a small black hole inside the accretion disk of a supermassive black hole. The small BH, if it exists, is between 100 to 10,000 solar masses. At the bottom of that range, it’s the same mass as a PBH. It’s not thought to be primordial, but it indicates how much we’ve yet to learn about black holes. Credit: Caltech/R. Hurt (IPAC)The researchers say that in their analysis of a population of both astrophysical and primordial binaries, PBHs cannot entirely comprise dark matter. At most, they can make up a small portion of it.
“… in a population of binaries consisting of primordial and astrophysical black holes, we find that, in every scenario, the PBHs can make up at most fPBH less than or equal to 10-3 of dark matter in the mass range 1-200 solar masses.”
fPBH represents the fraction of dark matter that PBHs can comprise, 10-3 means 0.001, and the solar mass range is self-explanatory. It doesn’t take a physicist to understand what they’re saying. PBHs can make up only a tiny fraction of dark matter in their analysis.
This may not be a headline-generating study. It’s a look under the hood of astrophysics and cosmology, where teams of researchers work hard to incrementally constrain and define different phenomena. But that doesn’t undermine its significance.
One day, there might be a headline that screams, “Physicists Identify Dark Matter! Universe’s Big Questions Answered!”
If that ever happens, hundreds and thousands of studies like this one will be behind it.
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Research Work Begins on the Habitable Worlds Observatory
NASA are planning on building a telescope to hunt for habitable worlds. The imaginatively named ‘Habitable Worlds Observatory’ is at least a decade away but NASA have started to develop the underlying technology needed. The contracts have been awarded to three companies to research the next-generation optics, mission designs and telescope features at a cost of $17.5 million. Work should begin late summer 2024.
The Habitable Worlds Observatory (HWO) is a mission to launch a large space telescope with the main purpose of directly imaging Earth-like planets around stars like our Sun. It will also be able to study their atmosphere to look for chemical signatures for signs of life. The mission is very much in its early planning stages with working groups looking at the science goals and how to achieve them.
This is an artist’s illustration of the exoplanet TRAPPIST-1d, a potentially habitable exoplanet about 40 light-years away. Image Credit: By NASA/JPL-Caltech – Cropped from: PIA22093: TRAPPIST-1 Planet Lineup – Updated Feb. 2018, Public Domain, https://commons.wikimedia.org/w/index.php?curid=76364484It is thought that, based on existing exoplanet research, one star in every five is likely to have an Earth-like planet in orbit around it. Of course the whole premise of searching for live in the Universe relies on that life being somewhat similar to our own. There may well be life based on a whole different chemistry but if we are to find life then we may as well look for life like ours rather thank take a punt on something completely different. To that end HWO will be on the lookout for chemicals like Oxygen and methane and other signatures that hint at the presence of life.
In January of this year, NASA requested proposals that will drive and advance the necessary technologies that will be needed for HWO. This may sound a simple ask but taking into consideration what will be needed such as a coronagraph thousands of times more capable than existing to block out light from the host star and an optical system that can remain stationary to the accuracy of the width of an atom during an observation and you realise the challenges ahead.
Following on from the first phase, NASA has now selected three proposals for two-year fixed price contracts that total a staggering $17.5 million. Sounds like a lot of money but Hubble cost $16 billion to develop and launch. The work is schedule to begin by late summer 2024. Together the contracts will deliver a framework of technology that will support the next phase of the HWO development and include;
- Modelling and sub-systems for an ultra-stable’ optical system far beyond current capability. This will be delivered by BAE Systems.
- Develop necessary integrated modelling infrastructure that can navigate and compare design interdependencies. This element will be delivered by Lockheed Martin
- Advance the technologies need to support telescope operations such as deployable optical baffles to reduce stray light ingress and structural support for the optical train. This final element will be delivered by Northrop Grumman.
NASA will of course be in control the whole way through and the output will enable them to plan for the development and build phase of the mission. The work is not being completed in isolation though as there are learnings from the James Webb Space Telescope and the future Nancy Grace Telescope too.
Source : NASA Awards Advance Technologies for Future Habitable Worlds Mission
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The JWST is Re-Writing Astronomy Textbooks
When the James Webb Space Telescope was launched at the end of 2021, we expected stunning images and illuminating scientific results. So far, the powerful space telescope has lived up to our expectations. The JWST has shown us things about the early Universe we never anticipated.
Some of those results are forcing a rewrite of astronomy textbooks.
Textbooks are regularly updated as new evidence works its way through the scientific process. But seldom does new evidence arrive at the speed the JWST is delivering it. Chapters on the Early Universe are in need of a significant update.
At the recent 2024 International Space Science Institute (ISSI) Breakthrough Workshop in Bern, Switzerland, a group of scientists summed up some of the telescope’s results so far. Their work is in a new paper titled “The First Billion Years, According to JWST.” The list of authors is long, and those authors are quick to point out that an even larger group of international scientists played a role. It takes an international scientific community to use JWST observations and advance the “collective understanding of the evolution of the Early Universe,” as the authors write.
The Early Universe is one of the JWST’s primary scientific targets. Its infrared capabilities allow it to see the light from ancient galaxies with greater acuity than any other telescope. The telescope was designed to directly address confounding questions about the high-redshift Universe.
The following three broad questions are foundational issues in cosmology that the JWST is addressing.
What are the Physical Properties of the Earliest Galaxies? The JWST captured these images of 19 face-on spiral galaxies as part of the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) program. The telescope has shown us that early galaxies were much larger than expected. Image Credit: NASA, ESA, CSA, STScI, J. Lee (STScI), T. Williams (Oxford), PHANGS Team, E. Wheatley (STScI)The early Universe and its transformations are fundamental to our understanding of the Universe around us today. Galaxies were in their infancy, stars were forming, and black holes were forming and becoming more massive.
The Hubble Space Telescope was limited to observations at about z=11. The JWST has shoved that boundary aside. Its current high-redshift observations have reached z=14.32. Astronomers think that the JWST will eventually observe galaxies at z=20.
The lookback time of extragalactic observations by their redshift up to z=20. Image Credit: By Sandizer – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=140812763The first few hundred million years after the Big Bang is called the Cosmic Dawn. JWST showed us that ancient galaxies during the Cosmic Dawn were much more luminous and, therefore, larger than we expected. The galaxy the telescope found at z=14.32, called JADES-GS-z14-0, has several hundred million solar masses. “This raises the question: How can nature make such a bright, massive, and large galaxy in less than 300 million years?” scientists involved with JWST Advanced Deep Extragalactic Survey (JADES) said in a NASA post.
It also showed us that they were differently shaped, that they contained more dust than expected, and that oxygen was present. The presence of oxygen indicates that generations of stars had already lived and died. “The presence of oxygen so early in the life of this galaxy is a surprise and suggests that multiple generations of very massive stars had already lived their lives before we observed the galaxy,” the researchers wrote in the post.
“All of these observations, together, tell us that JADES-GS-z14-0 is not like the types of galaxies that have been predicted by theoretical models and computer simulations to exist in the very early universe,” they continued.
What is the Nature of Active Galactic Nuclei in Early Galaxies? This image shows Hercules A, a galaxy in the Hercules constellation. The X-ray observations show superheated gas, and the radio observations show jets of particles streaming away from the AGN at the center of the galaxy. The jets are almost 1 million light-years long. Image Credits: X-ray: NASA/CXC/SAO; visual: NASA/STScI; radio: NSF/NRAO/VLA.Active Galactic Nuclei (AGN) are Supermassive Black Holes (SMBHs) that are actively accreting material and emitting jets and winds.
Quasars are a sub-type of AGN that are extremely luminous and distant, and quasar observations show that SMBHs were present in the centers of galaxies as early as 700 million years after the Big Bang. But their origins were a mystery. Astrophysicists think that these early SMBHs were created from black hole “seeds” that were either “light” or “heavy.” Light seeds had about 10 to 100 solar masses and were stellar remnants. Heavy seeds had 10 to 105 solar masses and came from the direct collapse of gas clouds.
The JWST’s ability to effectively look back in time has allowed it to spot an ancient black hole at about z=10.3 that contains between 107 to 108 solar masses. The Hubble Space Telescope didn’t allow astronomers to measure the stellar mass of entire galaxies the way that the JWST does. Thanks to the JWST’s power, astronomers know that the black hole at z=10.3 has about the same mass as the stellar mass of its entire galaxy. This is in stark contrast to modern galaxies, where the mass of the black hole is only about 0.1% of the entire stellar mass.
Such a massive black hole existing only about 500 million years after the Big Bang is proof that early BHs originated from heavy seeds. This is actually in line with theoretical predictions. So, the textbook authors are now in a position to remove the uncertainty.
When and How Did the Early Universe Become Ionized? This graphical timeline of the Universe shows where the Epoch of Reionization fits in. Image Credit: By NASA – NASA, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6272041“We know that hydrogen reionization happened, but exactly when and how it happened has been a major missing piece in our understanding of the first billion years.”
From “The First Billion Years According to the JWST.”We know that in the early Universe, hydrogen became ionized during the Epoch of Reionization (EoR). Light from the first stars, accreting black holes, and galaxies heated and reionized the hydrogen gas in the intergalactic medium (IGM), removing the dense, hot, primordial fog that suffused the early Universe.
Young stars were the primary light source for the reionization. They created expanding bubbles of ionized hydrogen that overlapped one another. Eventually, the bubbles expanded until the entire Universe was ionized.
This was a critical phase in the development of the Universe. It allowed future galaxies, especially dwarf galaxies, to cool their gas and form stars. But scientists aren’t certain how black holes, stars, and galaxies contributed to the reionization or the exact time frame in which it took place. “We know that hydrogen reionization happened, but exactly when and how it happened has been a major missing piece in our understanding of the first billion years,” the authors of the new paper write.
Astronomers knew that Reionization ended about one billion years after the Big Bang, at about redshift z=5-6. But before the JWST, it was difficult to measure the properties of the UV light that caused it. With the JWST’s advanced spectroscopic capabilities, astronomers have narrowed down the parameters of reionization. “We have found spectroscopically confirmed galaxies up to z = 13.2, implying reionization may have started just a few hundred million years after the Big Bang,” the authors write.
JWST results also show that accreting black holes and their AGN likely contributed no more than 25% of the UV light that caused reionization.
These results will require some rewriting of textbook chapters on the EOR, even though there are still lingering questions about it. “There is still significant debate about the primary sources of reionization, in particular, the contribution of faint galaxies,” the authors write. Even though the JWST is extraordinarily powerful, some distant, faint objects are beyond its reach.
The James Webb Space Telescope: humanity’s new favourite science instrument. Image Credit: NASAThe JWST is not even halfway through its mission and has already transformed our understanding of the Universe’s first one billion years. It was built to address questions around the Epoch of Reionization, the first black holes, and the first galaxies and stars. There’s definitely much more to come. Who knows what the sum total of its contributions will be?
As an astronomy writer, I’m extremely grateful to all of the people who brought the JWST to fruition. It took a long time to build, cost a lot more than expected, and was almost cancelled by Congress. Its perilous path to completion makes me even more grateful to be covering its results. The researchers using JWST data are clearly grateful, too.
“We dedicate this paper to the 20,000 people who spent decades to make JWST an incredible discovery machine,” they write.
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