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Astronomers have detected an intensely brightening and dimming quasar that may help explain how some objects in the early universe grew at a highly accelerated rate. The discovery is the most distant object detected by the NuSTAR X-ray space telescope (which launched in 2012) and stands as one of the most highly 'variable' quasars ever identified.

Supermassive black holes can have trillions of times more mass than the Sun, only exist in specific locations, and could number in the trillions. How can objects like that be hiding? They’re shielded from our view by thick columns of gas and dust.

However, astronomers are developing a way to find them: by looking for donuts that glow in the infrared.

It seems almost certain that large galaxies like our own Milky Way host supermassive black holes (SMBHs) in their centers. They grow through mergers with other SMBHs and through accretion. When they’re actively accreting material, they’re called Active Galactic Nuclei (AGN) and become so bright they can outshine all of the stars in their entire galaxy. The most luminous AGN are called quasars.

SMBHs, like all black holes, emit no light themselves. Instead, the light comes from the torus of swirling gas and dust that forms an accretion ring around the SMBH. The gas and dust become superheated and emit electromagnetic radiation. So far, scientists have only imaged two SMBHs, both with the Event Horizon Telescope (EHT). (To be clear, the EHT doesn’t actually “see” the SMBH. Instead, it sees the light coming from the accretion disk and the shadow the SMBH casts on the disk.)

The first ever actual image of a black hole was taken in 2019. This shows the black hole at the heart of galaxy M87. Image Credit: Event Horizon Telescope Collaboration

Even without seeing them, astronomers are pretty certain that most large galaxies host an SMBH. How? Stars near the center of galaxies move in unusual ways as if they’re under the influence of an extremely massive object. The intense radiation from AGN is also strong evidence of an SMBH. Galaxy formation and evolution models and gravitational lensing provide additional evidence.

However, astronomers still want to find more of them so they can confirm their models or adapt them to suit observational results. The problem is that many of them are hidden from view by gas and dust. If that gas and dust are thick and dense enough, they act as a veil, blocking even low-energy X-ray light. That means our view of the galaxy centre is obscured, even if it is an AGN.

Whether or not we can see the centre of a galaxy like this depends on our viewing. From a “side” view, the torus blocks it out, while from a “top” or “bottom” view, it doesn’t.

Astronomers want to understand how many SMBHs there are in the Universe, but obviously, there’s no way to find them and count them all. What they hope to do is determine the ratio between hidden and unhidden SMBHs. To do that, they need a large enough sample to extrapolate from. That way, they can get a more accurate idea of how many SMBHs there are.

A new survey using data from multiple NASA telescopes has advanced our understanding of SMBHs. The survey and its results are detailed in a paper titled “The NuSTAR Local AGN NH Distribution Survey (NuLANDS). I. Toward a Truly Representative Column Density Distribution in the Local Universe.” It’s published in The Astrophysical Journal, and the lead author is Peter G. Boorman, an astrophysicist from the Cahill Center for Astrophysics at the California Institute of Technology.

The NuLANDS aims to find the thick dust and gas that obscures AGN. Previous efforts to detect AGN have been hampered by relying on hard X-rays, the highest-energy portion of the X-ray spectrum, often defined as X-rays with energies greater than 10 kiloelectronvolts (keV). Accretion disks around SMBHs can be heated to extremely high temperatures and emit hard X-rays.

However, thick enough gas and dust can block even hard X-rays. If the column density of the gas is too high, no hard X-rays can get through. “Hard X-ray-selected samples of active galactic nuclei (AGN) provide one of the cleanest views of supermassive black hole accretion but are biased against objects obscured by Compton-thick gas column densities of NH > 1024 cm-2,” the authors write in their paper. Compton-thick means thick enough to obscure an AGN.

The thick gas and dust that block hard X-rays absorb them and then re-emit them as lower-energy infrared light. This creates a glowing torus, or donut, of gas and dust. This is where IRAS comes in.

IRAS was the Infrared Astronomical Satellite, launched in January 1983 and operated for 10 months. It performed an infrared survey of the entire sky, and it spotted the infrared emissions from the toruses around SMBHs. Critically, it spotted these toruses whether they were face-on or edge-on.

However, IRAS didn’t discriminate against infrared sources. It also spotted galaxies undergoing rapid star formation, which emit similar infrared light as AGN. In this new research, the authors used ground-based telescopes to differentiate between the two.

At that stage, the researchers had a sample of toruses around SMBHs emitting infrared light. However, they didn’t know if they were seeing them face-on or edge-on. Remember, their goal was to determine how many SMBHs are hidden and how many aren’t. With a large enough sample containing good data, they could extrapolate how many SMBHs there are and whether all large galaxies have one.

This is where another NASA satellite comes in. NuSTAR is an X-ray space telescope that was launched in June 2012 and is still operating. One of its primary goals was to detect SMBHs one billion times more massive than the Sun.

An artist’s illustration of NASA’s NuSTAR X-ray satellite. Image Credit: NASA/JPL-Caltech

NuSTAR can detect high-energy X-rays that pass through thick dust and gas, so it can detect edge-on SMBHs. However, it can use hours of observation time to detect these X-rays, so for it to be effective, it has to know where to look first. That’s what IRAS helped with.

“It amazes me how useful IRAS and NuSTAR were for this project, especially despite IRAS being operational over 40 years ago,” said lead author Boorman. “I think it shows the legacy value of telescope archives and the benefit of using multiple instruments and wavelengths of light together.”

In their NuLANDS survey, the researchers looked at 122 nearby AGN chosen for their warm infrared colours. “To tackle this issue, we present the NuSTAR Local AGN NH Distribution Survey (NuLANDS)—a legacy sample of 122 nearby (z < 0.044) AGN primarily selected to have warm infrared colors from IRAS between 25 and 60 ?m,” the authors write.

Their sample of galaxies is also biased towards those whose AGN is obscured by something close to them rather than by some large-scale feature of the galaxy itself. “By construction, our sample will miss sources affected by severe narrow-line reddening, and thus segregates sources dominated by small-scale nuclear obscuration from large-scale host-galaxy obscuration,” the authors explain.

The researchers found that 35% ± 9% of galaxies have Compton-thick dust, meaning their AGN and SMBH are obscured. So, about one-third of the Universe’s SMBHs are obscured. However, these are only the first results from NuLANDS, and while 122 AGN is a sizeable survey, there’s more to come.

These results support some of the thinking around SMBHs, their masses, and their numbers. SMBHs must consume an enormous amount of material to reach their enormous sizes. That means many of them should be obscured by the very dust they’ll eventually consume. Boorman and his co-authors say their results support this idea.

“If we didn’t have black holes, galaxies would be much larger,” said study co-author Poshak Gandhi, a professor of astrophysics at the University of Southampton in the UK. That’s for two reasons. First, they consume material that would otherwise form more stars. Second, sometimes too much material falls toward the black hole, and they belch up the excess. That ejected material can disperse the clouds of gas where stars form, slowing the galaxy’s star formation.

“So if we didn’t have a supermassive black hole in our Milky Way galaxy, there might be many more stars in the sky. That’s just one example of how black holes can influence a galaxy’s evolution,” said Gandhi.

The post About a Third of Supermassive Black Holes are Hiding appeared first on Universe Today.

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Water is the essence of life. Every living thing on Earth contains water within it. The Earth is rich with life because it is rich with water. This fundamental connection between water and life is partly due to water’s extraordinary properties, but part of it is due to the fact that water is one of the most abundant molecules in the Universe. Made from one part oxygen and two parts hydrogen, its structure is simple and strong. The hydrogen comes from the primordial fire of the Big Bang and is by far the most common element. Oxygen is created in the cores of large stars, along with carbon and nitrogen, as part of the CNO fusion cycle.

Because of its origin, we’ve generally thought that oxygen (and correspondingly water) grew in abundance over time. From the first stars to the present day, each generation cast oxygen into space in its dying moments. So, while water was rare in the early Universe, it is relatively common now. But a new study suggests that isn’t the case.

Astronomers categorize stars into populations depending on their age and metallicity, where “metals” are any elements other than hydrogen and helium. The youngest and most metal-rich stars, such as the Sun, are called Population I. Older stars with fewer metals are Population II. The oldest stars, the very first stars to appear in the Universe, are known as Population III. Though we haven’t observed Pop III stars directly, they would have been enormous stars made entirely of hydrogen and helium. The first seeds of everything we see around us, from oceans to trees to beloved friends, formed within these first stars. A new study on the arXiv argues that Pop III stars also flooded the cosmos with water.

In their study, the team modeled the explosions of small (13 solar mass) and large (200 solar mass) early stars. The large stars would have been the very first stars formed from primordial clouds, while the smaller stars would have been the first stars to form in early stellar nurseries. Not quite Pop III stars, but with very low metallicity. When the smaller stars died, they exploded as typical supernovae, but when the large stars died, they exploded as brilliant pair-instability supernovae.

Based on simulations, these stars would have greatly enriched the environment with water. The molecular clouds formed from the remnants of these stars had 10 to 30 times the water fraction of diffuse molecular clouds seen in the Milky Way today. Based on this, the team argues that by 100 to 200 million years after the Big Bang, there was enough water and other elements in molecular clouds for life to form.

Whether life actually did appear in the Universe so early is an unanswered question. There is also the fact that while water formed early, ionization and other astrophysical processes may have broken up many of these molecules. Water might have been plentiful early on, but the Universe entered a dry period before Pop II and Pop I stars generated the water levels we see today. But it’s possible that much of the water around us came from the very first stars.

Reference: Whalen, Daniel J., Muhammad A. Latif, and Christopher Jessop. “Abundant Water from Early Supernovae at Cosmic Dawn.” arXiv preprint arXiv:2501.02051 (2025).

The post The First Supernovae Flooded the Early Universe With Water appeared first on Universe Today.