Some Clever Ways to Search for Primordial Black Holes

Primordial Black Holes (PBHs) have recently received much attention in the physics community. One of the primary reasons is the potential link to dark matter. In effect, if PBHs can be proven to exist, there’s a very good chance that they are what dark matter, the invisible thing that makes up 85% of the universe’s mass, is made of. If proven, that would surely be a Nobel-level discovery in astrophysics. 

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Roman Space Telescope Will Be Hunting For Primordial Black Holes

This artist's illustration shows what primordial black holes might look like. In reality, the black holes would struggle to form accretion disks. (But without them it would just be an illustration of black space.) Image Credit: NASA’s Goddard Space Flight Center

When astrophysicists observe the cosmos, they see different types of black holes. They range from gargantuan supermassive black holes with billions of solar masses to difficult-to-find intermediate-mass black holes (IMBHs) all the way down to smaller stellar-mass black holes.

But there may be another class of these objects: primordial black holes (PBHs) that formed in the very early Universe. If they exist, the Nancy Grace Roman Space Telescope should be able to spot them.

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The World's Largest Digital Camera is Complete. It Will Go Into the Vera Rubin Observatory

Researchers examine the LSST Camera. The camera will soon be shipped to Chile, where it will be the heart of Vera C. Rubin Observatory (right). Credit: Vera C. Rubin Observatory/DOE/SLAC

The Vera C. Rubin Observatory, formerly the Large Synoptic Survey Telescope (LSST), was formally proposed in 2001 to create an astronomical facility that could conduct deep-sky surveys using the latest technology. This includes a wide-field reflecting telescope with an 8.4-meter (~27.5-foot) primary mirror that relies on a novel three-mirror design (the Simonyi Survey Telescope) and a 3.2-megapixel Charge-Coupled Device (CCD) imaging camera (the LSST Camera). Once complete, Rubin will perform a 10-year survey of the southern sky known as the Legacy Survey of Space and Time (LSST).

While construction on the observatory itself did not begin until 2015, work began on the telescope’s digital cameras and primary mirror much sooner (in 2004 and 2007, respectively). After two decades of work, scientists and engineers at the Department of Energy’s (DOE) SLAC National Accelerator Laboratory and their collaborators announced the completion of the LSST Camera – the largest digital camera ever constructed. Once mounted on the Simonyi Survey Telescope, this camera will help researchers observe our Universe in unprecedented detail.

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A New, More Accurate Measurement for the Clumpiness of the Universe

Clusters of galaxies as observed by the eROSITA instrument. Colors indicate the redshift of the clusters, up to about 9 billion years of lookback time. Credit: MPE, J. Sanders for the eROSITA consortium.
Clusters of galaxies as observed by the eROSITA instrument. The idea is to determine the clumpiness (or distribution) of matter in the Universe. Colors indicate the redshift of the clusters, up to about 9 billion years of lookback time. Credit: MPE, J. Sanders for the eROSITA consortium.

Cosmologists are wrestling with an interesting question: how much clumpiness does the Universe have? There are competing but not compatible measurements of cosmic clumpiness and that introduces a “tension” between the differing measurements. It involves the amount and distribution of matter in the Universe. However, dark energy and neutrinos are also in the mix. Now, results from a recent large X-ray survey of galaxy clusters may help “ease the tension”.

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Euclid Begins its 6-Year Survey of the Dark Universe

The areas that the space telescope Euclid will observe. Credit: ESA/Euclid/Euclid Consortium

On July 1, 2023, the Euclid Spacecraft launched with a clear mission: to map the dark and distant Universe. To achieve that goal, over the next 6 years, Euclid will make 40,000 observations of the sky beyond the Milky Way. From this data astronomers will be able to map the positions of billions of galaxies, allowing astronomers to observe the effects of dark matter.

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How Does the Cosmic Web Drive Galaxy Evolution?

A computer simulation of what gas and stars in a galaxy cluster look like, and how they look embedded in the cosmic web. The assembly of galaxy clusters has implications for the clumpiness of the Universe throughout time. Credit: Yannick Bahé.
A computer simulation of what gas and stars in a galaxy cluster look like, and how they look embedded in the cosmic web. The assembly of galaxy clusters has implications for the clumpiness of the Universe throughout time. Credit: Yannick Bahé.

Galaxies experience a long strange trip through the cosmic web as they grow and evolve. It turns out that the neighborhoods they spend time in on the journey change their evolution, and that affects their star formation activity and alters their gas content.

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Dust Ruins Another Way of Measuring Distance in the Universe

A dusty spiral galaxy known as M66. Credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble

Astronomers have many ways to measure the distance to galaxies billions of light years away, but most of them rely upon standard candles. These are astrophysical processes that have a brightness we can calibrate, such as Cepheid variable stars or Type Ia supernovae. Of course, all of these standard candles have some inherent variability, so astronomers also look for where our assumptions about them can lead us astray. As a case in point, a recent study in The Astrophysical Journal shows how galactic dust can bias distance observations.

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The JWST Solves the Mystery of Ancient Light

This image shows the galaxy EGSY8p7, a bright galaxy in the early Universe where light emission is seen from, among other things, excited hydrogen atoms — Lyman-alpha emission. The galaxy was identified in a field of young galaxies studied by Webb in the CEERS survey. In the bottom two panels, Webb’s high sensitivity picks out this distant galaxy along with its two companion galaxies, where previous observations saw only one larger galaxy in its place. This discovery of a cluster of interacting galaxies sheds light on the mystery of why the hydrogen emission from EGSY8p7, shrouded in neutral gas formed after the Big Bang, should be visible at all. Image Credit: ESA/Webb, NASA & CSA, S. Finkelstein (UT Austin), M. Bagley (UT Austin), R. Larson (UT Austin), A. Pagan (STScI), C. Witten, M. Zamani (ESA/Webb)

The very early Universe was a dark place. It was packed with light-blocking hydrogen and not much else. Only when the first stars switched on and began illuminating their surroundings with UV radiation did light begin its reign. That occurred during the Epoch of Reionization.

But before the Universe became well-lit, a specific and mysterious type of light pierced the darkness: Lyman-alpha emissions.

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Astronomers Rule Out One Explanation for the Hubble Tension

One of the brightest Cepheid variable stars, RS Puppis. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration

Perhaps the greatest and most frustrating mystery in cosmology is the Hubble tension problem. Put simply, all the observational evidence we have points to a Universe that began in a hot, dense state, and then expanded at an ever-increasing rate to become the Universe we see today. Every measurement of that expansion agrees with this, but where they don’t agree is on what that rate exactly is. We can measure expansion in lots of different ways, and while they are in the same general ballpark, their uncertainties are so small now that they don’t overlap. There is no value for the Hubble parameter that falls within the uncertainty of all measurements, hence the problem.

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1,500 New Type 1A Supernova Found as Part of the Dark Energy Survey

An example of a supernova discovered by the Dark Energy Survey within the field covered by one of the individual detectors in the Dark Energy Camera. The supernova exploded in a spiral galaxy with redshift = 0.04528, which corresponds to a light-travel time of about 0.6 billion years. In comparison, the quasar at the right has a redshift of 3.979 and a light-travel time of 11.5 billion years. Image Credit: DES Collaboration/NOIRLab/NSF/AURA/M. Zamani

Supernova explosions are fascinating because they’re so cataclysmic, powerful, and awe-inspiring. They’re Nature’s summer blockbusters. Humans have recorded their existence in ancient astronomical records and stone carvings, and in our age, with telescopes.

Now, the Dark Energy Survey (DES) has uncovered the largest number of Type 1A supernovae ever found with a single telescope.

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