The time to catch Comet T4 Lemmon is now, before it vanishes for another 36,000 years.
Often, icy interlopers creep up on the inner solar system, only to once again vanish into the abyss. Such is the case with long-period comet C/2021 T4 Lemmon, headed towards perihelion early next week.
The comet was discovered by the Catalina Sky Survey based on Mount Lemmon outside of Tucson, Arizona on the night of October 7th, 2021, slowly moving through the constellation of Taurus the Bull. Shining at magnitude +20 and 6.4 Astronomical Units (AU, 595 million miles or 958 million kilometers) distant out past the orbit of Jupiter at the time of discovery, astronomers soon realized that Comet T4 Lemmon could be a moderately bright binocular object in the summer of 2023.
The orbit of Comet T4 Lemmon, showing the comet near perihelion. Credit: NASA/JPL.
And here we are. The comet is also on a steep 160 inclination orbit, moving backwards or retrograde versus the planets in the inner solar system. Curiously, the comet may also be a first-time visitor from the Oort Cloud. On an orbit with a 1.000034 eccentricity inbound and a period most likely measured in millions of years, the comet’s orbit was altered into a 36,000-year return period outbound, due to a 0.869 AU encounter with Jupiter during the current passage.
The 2023 apparition for Comet T4 Lemmon starts the end of July, in the southern constellation of Ara the Altar. Currently shining at +8th magnitude, we’ve already seen some fine shots of the comet taken from the southern hemisphere in June and July 2023. We’re fortunate that the comet is visiting the inner solar system when it is, as it just passed 0.54 AU (81 million kilometers) from the Earth on July 21st. Comet T4 Lemmon crossed opposition on July 18th moving from the morning to the evening sky, and bottomed out on July 20th at a southern declination of -56 degrees. The comet is currently moving at three degrees per day across the sky (about the diameter of six Full Moons a day) as it slowly recedes from the Earth.
Comet T4 Lemmon from June 30th, as it threads between the wide double stars of Kappa Sculptoris. Credit: Pepe Chambó/Cometografia.
Comet T4 Lemmon is currently a bashful one for northern hemisphere observers, but don’t despair; the view improves going in to August as the comet creeps up towards the ecliptic. For example, Tampa, Florida sees the comet low to the south (20 degrees above the southern horizon) after dusk on August 1st.
Meanwhile, Cape Town South Africa sees the comet a generous 70 degrees above the southern horizon on the same date.
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If You Could See Gravitational Waves, the Universe Would Look Like This
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.
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
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?
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.
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.
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.
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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