Cosmology Archives

December 8, 2023December 8, 2023 by Matt Williams

If Our Part of the Universe is Less Dense, Would That Explain the Hubble Tension?

Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos. Credit: NSF/DES/NOIRLab/DOE/FNAL/AURA/University of Alaska Anchorage/

In the 1920s, Edwin Hubble and Georges Lemaitre made a startling discovery that forever changed our perception of the Universe. Upon observing galaxies beyond the Milky Way and measuring their spectra, they determined that the Universe was expanding. By the 1990s, with the help of the Hubble Space Telescope, scientists took the deepest images of the Universe to date and made another startling discovery: the rate of expansion is speeding up! This parameter, denoted by Lambda, is integral to the accepted model of cosmology, known as the Lambda Cold Dark Matter (LCDM) model.

Since then, attempts to measure distances have produced a discrepancy known as the “Hubble Tension.” While it was hoped that the James Webb Space Telescope (JWST) would resolve this “crisis in cosmology,” its observations have only deepened the mystery. This has led to several proposed resolutions, including the idea that there was an “Early Dark Energy” shortly after the Big Bang. In a recent paper, an international team of astrophysicists proposed a new solution based on an alternate theory of gravity that states that our galaxy is in the center of an “under-density.”

November 10, 2023November 10, 2023 by Brian Koberlein

If We Could Find Them, Primordial Black Holes Would Explain a Lot About the Universe

Artist view of small black holes in the accretion disk of a supermassive black hole. Credit: Caltech/R. Hurt (IPAC)

There are three known types of black holes in the Universe: supermassive black holes that lurk in the centers of galaxies, stellar-mass black holes that are the remnants of massive stars, and intermediate-mass black holes that can be found in dense clusters of stars. But there is a fourth, hypothetical type of black hole known as primordial black holes (PBHs). If they exist, they could solve a few cosmological mysteries.

October 27, 2023October 27, 2023 by Nancy Atkinson

Everything in the Universe Fits in This One Graph. Even the Impossible Stuff

Masses, sizes, and relative densities of objects in our Universe, and more. Credit: Charles H. Lineweaver & Vihan M. Patel, doi: 10.1119/5.0150209.

The Universe has physical constants, such as the force of gravity that define everything. If these constants were any different, our Universe would look quite different. When you consider the types of objects that exist in our Universe – from quarks and bacteria to fleas and superclusters — different forces dominate their existence.

A fascinating new graph plots everything in the known Universe and shows us what’s possible. It also shows what types of objects are prohibited by the laws of physics as we understand them.

October 24, 2023October 24, 2023 by Brian Koberlein

A Fast Radio Burst Took 8 Billion Years to Reach Us

Illustration of the path of the fast radio burst FRB 20220610A to Earth. Credit: ESO/M. Kornmesser

Fast Radio Bursts are an astrophysical enigma. They are intense bursts of radio energy lasting anywhere from a fraction of a millisecond to a few seconds, typically with a frequency of around 1,400 MHz, and we still don’t know what causes them. They were first detected in 2007 but were initially so rare and short-lived that it was difficult to confirm they weren’t terrestrial in origin. With the inauguration of the CHIME telescope and other wide-field radio observatories, we started observing lots of them, which confirmed they were both astrophysical and mostly coming from outside our galaxy. Now one has been observed from a galaxy 8 billion light years away, and it could help us solve a cosmological mystery.

October 5, 2023October 5, 2023 by Laurence Tognetti

The Big Bang: What is it? Why study it? What happened before? How will it all end?

Approximately 13.8 billion years ago, the greatest event in all of existence occurred that literally created existence itself. This event is known as the Big Bang, and it’s responsible for the estimated septillion number of stars that are scattered across the vast reaches of the unknown, including the one our small, blue world orbits. However, other than knowing that the Big Bang occurred, there is still a septillion amount of information we still don’t know about the greatest event in the history of existence.

September 5, 2023September 5, 2023 by Brian Koberlein

A New Telescope Could Detect Decaying Dark Matter in the Early Universe

The Hydrogen Epoch of Reionization Array (HERA). Credit: HERA Collaboration

Hydrogen is the most abundant element in the Universe. By far. More than 90% of the atoms in the Universe are hydrogen. Ten times the number of helium atoms, and a hundred times more than all other elements combined. It’s everywhere, from the water in our oceans to the earliest regions of the Cosmic Dawn. Fortunately for astronomers, all this neutral hydrogen can emit a faint emission line of radio light.

August 16, 2023August 16, 2023 by Brian Koberlein

New Horizons is So Far Away, it Can Measure the True Darkness of the Universe

Artist view of the New Horizons spacecraft against a sea of stars. Credit: Serge Brunier/Marc Postman/Dan Durda

Just how dark is the night sky?

If you step outside during a moonless night and look up, it probably doesn’t look that dark at all. Streetlights or nearby porch lights fill the air with a background glow, particularly if they happen to be bluish-white LEDs. Light pollution in your neighborhood is likely so bad that you can only see a few bright stars. Even in somewhat rural areas, our skies are so bright that the Milky Way isn’t really visible. In North America and Europe, only about a quarter of children have seen the Milky Way.

July 6, 2023July 6, 2023 by Brian Koberlein

Did the Pulsar Timing Array Actually Detect Colliding Primordial Black Holes?

Illustration of merging black holes and their effect on pulsars and Earth. Credit: Daniëlle Futselaar (artsource.nl) / Max Planck Institute for Radio Astronomy

The universe is filled with gravitational waves. We know this thanks to the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), which recently announced the first observations of long wavelength gravitational waves rippling through the Milky Way. The waves are likely caused by the mergers of supermassive black holes, but can we prove it?

June 28, 2023June 28, 2023 by Matt Williams

Two New Space Telescopes Will Bring Dark Energy Into Focus

High-resolution illustration of the Euclid and Roman spacecraft against a starry background. Credits: NASA’s Goddard Space Flight Center, ESA/ATG medialab

Since the 1990s, thanks to observations by the venerable Hubble Space Telescope (HST), astronomers have contemplated the mystery of cosmic expansion. While scientists have known about this since the late-1920s and early-30s, images acquired by Hubble‘s Ultra Deep Fields campaign revealed that the expansion has been accelerating for the past six billion years! This led scientists to reconsider Einstein’s theory that there is an unknown force in the Universe that “holds back gravity,” which he named the Cosmological Constant. To astronomers and cosmologists today, this force is known as “Dark Energy.”

However, not everyone is sold on the idea of Dark Energy, and some believe that cosmic expansion could mean there is a flaw in our understanding of gravity. In the near future, scientists will benefit from next-generation space telescopes to provide fresh insight into this mysterious force. These include the ESA’s Euclid mission, scheduled for launch this July, and NASA’s Nancy Grace Roman Space Telescope (RST), the direct successor to Hubble that will launch in May 2027. Once operational, these space telescopes will investigate these competing theories to see which holds up.

June 23, 2023June 23, 2023 by Brian Koberlein

Nancy Grace Roman Could Detect Supermassive Dark Stars

Artist view dark neutron star. Credit: NASA's Goddard Space Flight Center Conceptual Image Lab

The first stars of the universe were very different than the stars we see today. They were made purely of hydrogen and helium, without heavier elements to help them generate energy in their core. As a result, they were likely hundreds of times more massive than the Sun. But some of the first stars may have been even stranger. In the early universe, dark matter could have been more concentrated than it is now, and it may have powered strange stellar objects known as dark stars.