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When the James Webb Space Telescope started collecting data, it gave us an unprecedented view of the distant cosmos. Faint, redshifted galaxies seen by Hubble as mere smudges of light were revealed as objects of structure and form. And astronomers were faced with a bit of a problem. Those earliest galaxies seemed too developed and too large to have formed within the accepted timeline of the universe. This triggered a flurry of articles claiming boldly that JWST had disproven the big bang. Now a new article in the Monthly Notices of the Royal Astronomical Society argues that the problem isn’t that galaxies are too developed, but rather that the universe is twice as old as we’ve thought. A whopping 26.7 billion years old to be exact. It’s a bold claim, but does the data really support it?

The model proposed in the paper begins with something known as tired light. In the tired light model, light spontaneously loses energy over time. So as photons travel billions of light years through the cosmos, they become redshifted. Thus, the light of distant galaxies is redshifted not because of cosmic expansion, but because of the inherent reddening of light over time. The idea of tired light has been around since Edwin Hubble first observed cosmic expansion as a way to maintain the idea of a steady-state universe. It lost popularity as the evidence for cosmic expansion became clear, and regained some popularity as the Webb observations started rolling in.

We’ve long known that tired light doesn’t work on its own, so this paper adds a new twist dealing with universal physical constants. Quantities such as the speed of light, the charge of an electron, or the gravitational constant seem to be built into the structure of the universe. They have the values they do because of the way the universe formed, and it’s generally assumed they don’t change over time. We have geological and astronomical observations that show physical constants haven’t changed for at least several few billion years.

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Cosmic Microwave Background observations don’t match tired light. Credit: Ned Wright

But this new paper argues that if you combine tired light and changing physical constants, you can get a universe that appears younger than it actually is. Basically, tired light gives you the cosmological redshift you observe, and gradually shifting physical constants means those mature distant galaxies aren’t just 100 million years old, they are billions of years old. By tweaking tired light and variable physical constants just so to match the data, you get a universe that is 26.7 billion years old.

Does the model work? Yes, but there are two problems with it. The first is that tweak theories are weak theories. While this model can be made to fit observational data, there’s no physical motivation for doing it. There are lots of models that can be tweaked to fit data, which is not the same as having a robust physical model. The author of the work argues that there could be some underlying mechanism that causes tired light and the physical constants to shift in just the right way, but there is still a lot of fudging in the model.

The second problem is that JWST’s observations don’t rule out the standard 13.7 billion-year-old universe. The galaxies are more complex than some computer simulations have predicted, but that’s not surprising given the limits of large structure models. There are plenty of ways early galaxies could have evolved quickly that don’t require rewriting cosmology.

But even without a strong physical motivation to create this model, the work is still useful. It’s the kind of paper that thinks outside the box, which is a great way to make sure we aren’t locked into old models just because they’ve worked so far. It isn’t likely that this new model overturns standard cosmology, but as long as ideas are testable and disprovable, as this model is, there is no harm in adding it to the pile of ideas.

Reference: Gupta, R. “JWST early Universe observations and ?CDM cosmology.” Monthly Notices of the Royal Astronomical Society (2023): stad2032.

The post The Universe Could Be Twice As Old if Light is Tired and Physical Constants Change appeared first on Universe Today.

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If You Could See Gravitational Waves, the Universe Would Look Like This

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September 22, 2023

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Imagine if you could see gravitational waves.

Of course, humans are too small to sense all but the strongest gravitational waves, so imagine you were a great creature of deep space, with tendrils that could extend a million kilometers. As gravitational waves rippled across your vast body, you would sense them squeezing and tugging ever so slightly upon you. And your brilliant mind could use these sensations to create an image in your mind. The ripples of distant supernovae, merging black holes, the undercurrent of the gravitational background. Creation, and destruction, all seen in your mind’s eye.

Perhaps there is such a creature in the vastness of space, but we humans must rely upon our intelligence and engineering. And we may achieve such a vision of the cosmos through a gravitational wave observatory such as the Laser Interferometer Space Antenna, or LISA.

Similar to LIGO, LISA will detect gravitational waves by bouncing laser light along extended arms, measuring the minuscule variations in arms length. But while LIGO has arms just 4 kilometers long, LISA could have arms millions of kilometers long. Where LIGO can detect powerful transient bursts of gravitational waves with frequencies under a kilohertz, such as the mergers of black holes, LISA will detect millihertz waves and will be able to detect not just black hole mergers, but the gradual inspiraling of supermassive black holes and possibly even the remnant gravitational waves of the big bang.

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Artist’s impression of the Laser Interferometer Space Antenna (LISA). Credit: ESA

With all this data, astronomers will be able to create a picture of the gravitational wave sky, just as radio astronomers can create images from radio light. If you wonder what the gravitational sky might look like, we now have an idea thanks to a recent study.

The team looked at various known gravitational wave sources such as binary white dwarf, neutron stars, and merging black holes, and calculated the frequencies and magnitudes of their gravitational waves. They then filtered these sources through the estimated limits of what LISA and a second proposed telescope the Advanced MilliHertz Gravitational-wave Observatory (AMIGO) should detect. From this, they assigned colors to various frequency ranges to create a false-color image of the sky. You can see this image above.

We’re still a decade or more away from the launch of LISA, so it will be a while before we can see the real image of the gravitational sky. But that image is out there right now. It ripples through all of us and has every day of our lives. If we’re patient and clever, it’s only a matter of time until we finally see those waves upon our cosmic shore.

Reference: Szekerczes, Kaitlyn, et al. “Imaging the Milky Way with Millihertz Gravitational Waves.” The Astronomical Journal 166.1 (2023): 17.

The post If You Could See Gravitational Waves, the Universe Would Look Like This appeared first on Universe Today.

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Solar Sails Could Reach Mars in Just 26 Days

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September 22, 2023

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A recent study submitted to Acta Astronautica explores the potential for using aerographite solar sails for traveling to Mars and interstellar space, which could dramatically reduce both the time and fuel required for such missions. This study comes while ongoing research into the use of solar sails is being conducted by a plethora of organizations along with the successful LightSail2 mission by The Planetary Society, and holds the potential to develop faster and more efficient propulsion systems for long-term space missions.

“Solar sail propulsion has the potential for rapid delivery of small payloads (sub-kilogram) throughout the solar system,” Dr. René Heller, who is an astrophysicist at the Max Planck Institute for Solar System Research and a co-author on the study, tells Universe Today. “Compared to conventional chemical propulsion, which can bring hundreds of tons of payload to low-Earth orbit and deliver a large fraction of that to the Moon, Mars, and beyond, this sounds ridiculously small. But the key value of solar sail technology is speed.”

Unlike conventional rockets, which rely on fuel in the form of a combustion of chemicals to exert an external force out the back of the spacecraft, solar sails don’t require fuel. Instead, they use sunlight for their propulsion mechanism, as the giant sails catch solar photons much like wind sails catching the wind when traveling across water. The longer the solar sails are deployed, the more solar photons are captured, which gradually increases the speed of the spacecraft.

For the study, the researchers conducted simulations on how fast a solar sail made of aerographite with a mass up to 1 kilogram (2.2 pounds), including 720 grams of aerographite with a cross-sectional area of 104 square meters, could reach Mars and the interstellar medium, also called the heliopause, using two trajectories from Earth known as direct outward transfer and inward transfer methods, respectively.

The direct outward transfer method for both the trip to Mars and the heliopause involved the solar sail both deploying and departing directly from a polar orbit around the Earth. The researchers determined that Mars being in opposition (directly opposite Earth from the Sun) at the time of solar sail deployment and departure from Earth would yield the best results for both velocity and travel time. This same polar orbit deployment and departure was also used for the heliopause trajectory, as well. For the inward transfer method, the solar sail would be delivered to approximately 0.6 astronomical units (AU) from the Sun via traditional chemical rockets, where the solar sail would deploy and begin its journey to either Mars or the heliopause. But how does an aerographite solar sail make this journey more feasible?

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Image taken by The Planetary Society’s LightSail 2 on 25 November 2019 during its mission orbiting the Earth. The curved appearance of the sails is from the spacecraft’s 185-degree fisheye camera lens, and the image was processed with color-correction along with removal of parts of the distortion. (Credit: The Planetary Society)

“With its low density of 0.18 kilograms per cubic meter, aerographite undercuts all conventional solar sail materials,” Julius Karlapp, who is a Research Assistant at the Dresden University of Technology and lead author of the study, tells Universe Today. “Compared to Mylar (a metallized polyester foil), for example, the density is four orders of magnitude smaller. Assuming that the thrust developed by a solar sail is directly dependent on the mass of the sail, the resulting thrust force is much higher. In addition to the acceleration advantage, the mechanical properties of aerographite are amazing.”

Through these simulations, the researchers found the direct outward transfer method and inward transfer method resulted in the solar sail reaching Mars in 26 days and 126 days, respectively, with the first 103 days being the travel time from Earth to the deployment point at 0.6 AU. For the journey to the heliopause, both methods resulted in 5.3 years and 4.2 years, respectively, with the first 103 days of the inward transfer method also being devoted to the travel time from the Earth to the deployment point at 0.6 AU, as well. The reason the heliopause is reached in a
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Dark Photons Could Be the Key to Both Dark Matter and the Muon Anomaly.

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September 21, 2023

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If dark matter exists, then where are the particles?

This single question threatens to topple the standard cosmological model, known as the LCDM model. The CDM stands for cold dark matter, and according to the model makes up nearly 85% of matter in the universe. It should be everywhere, and all around us, and yet every single search for dark matter particles has come up empty. If dark matter particles are real, we know what they are not. We don’t know what they are.

There are lots of ideas, from WIMPs to axions to sterile neutrinos, and none of them have shown up in our detectors. But one of the problems could be that while dark matter particles are everywhere, their particle mass is much higher than we can detect in our particle accelerators and neutrino observatories. If that’s the case, we may never observe them directly. But we might be able to detect the force that allows them to interact.

In particle physics, each fundamental force has one or more carrier bosons. Electromagnetism has the photon, the strong force has the gluons, the weak force has W & Z bosons, the gravitational force the graviton. Dark matter interacts gravitationally, but it also may interact via a dark force, which should have a carrier boson known as the dark photon.

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A hypothetical dark photon interaction. Credit: APS/Alan Stonebraker

Dark photons turn up in a generalization of the standard model of particle physics. According to theory, they would interact with dark matter similar to the way photons interact with charged particles. But just as the weak force and electromagnetism are connected as the electroweak force, this dark force and electromagnetism would be connected as a kind of electrodark force. What this means is that regular photons and dark photons could mix slightly, allowing dark matter to interact with regular matter very slightly. Although photons have no mass, dark photons would have mass. This means they would only interact over very short distances, and could quickly decay into other particles. Like the gluons of the strong force, we can’t observe them directly, but we can observe how they cause particles to interact. This is where a new study on dark photons comes in.

The authors analyze the dark photon model in two ways. The first is to use experimental data to constrain the physical parameters of dark photons, such as their mass and how strongly they mix with regular photons. The second is to compare a particle physics model with and without dark photons to key experimental results. In general, the study finds that the dark photon model is a better fit than the standard model, but it’s a particularly good fit for an experiment known as the anomalous magnetic moment of the gluon, or g-2.

The muon is a heavier sibling of the electron, and like the electron, it has an electric charge and a magnetic moment, or g-factor. The value of the muon g-factor is almost, but not exactly, equal to 2. The “not exactly” part, g – 2, is one of the most precisely measured values in particle physics. It is also one of the most precisely calculated values in particle theory. And they don’t agree.

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Experiment vs theory for g – 2. Credit: Ryan Postel, Fermilab/Muon g-2 collaboration

Experimentally, g-2 = 0.00233184121. Theoretical calculations put g-2 = 0.00233183620. This is known as the g-2 anomaly and is beyond irksome. If you include dark photon interactions, the theoretical result becomes g-2 = 0.00233183939, which is significantly better. Overall, the dark photon model is preferred over the standard model at 6.5 sigma, which is a very strong result.

All of this is very interesting, but we should add a few caveats. The first is

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