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Buried in the treasure trove of the Gaia catalog were two strange black hole systems. These were black holes orbiting sun-like stars, a situation that astronomers long thought impossible. Recently a team has proposed a mechanism for creating these kinds of oddballs.

The two black holes, dubbed BH1 and BH2, are each almost ten times the mass of the Sun. That’s not too unusual as black holes go, but what makes these systems strange is that they each have a companion star with roughly the same properties as the Sun. And those stars are orbiting on very wide orbits.

The problem with this setup is that typically sun-like stars don’t survive the transition of a companion turning into a black hole. The end of a giant star’s life is generally violent. When they die, they tend to either eject their smaller companion from the system completely, or just outright swallow them. Either way, we don’t expect small stars to orbit black holes.

But now researchers have a potential solution. They tracked the evolution of extremely massive stars, no smaller than 80 times the mass of the Sun. They found at the end of their lives they eject powerful winds that siphon off enormous amounts of material. This prevents the star from swelling so much that it just swallows its smaller companion. Eventually the star goes supernova and leaves behind a black hole.

Then the researchers studied just how common this kind of scenario is. They found many cases where a sun-like star with a wide enough orbit could survive this transition phase. The key is that the strong winds coming from the larger star have to be powerful enough to limit its late stage violence while still weak enough to not affect the smaller star. The researchers found that this was a surprisingly common scenario and could easily explain the existence of BH2 and BH2.

Based on these results the researchers believe that there might be hundreds of such systems in the Gaia data set that have yet to be discovered. It turns out that the universe is always surprising us and always much more clever than we could ever realize.

The post Sun-Like Stars Around Black Holes: What Gives? appeared first on Universe Today.

Particle physicists describe how elementary particles behave using a set of equations called their “Standard Model.” How did they become so confident that a set of math formulas, ones that can be compactly summarized on a coffee cup, can describe so much of nature?

My previous “Celebrations of the Standard Model” (you can find the full set here) have included the stories of how we know the strengths of the forces, the number of types (“flavors” and “colors”) and the electric charges of the quarks, and the structures of protons and neutrons, among others. Along the way I explained how W bosons, the electrically charged particles involved in the weak nuclear force, quickly decay (i.e. disintegrate into other particles). But I haven’t yet explained how their cousin, the electrically-neutral Z boson, decays. That story brings us to a central feature of the Standard Model.

Here’s the big picture. There’s a super-important number that plays a central role in the Standard Model. It’s a sort of angle (in a sense that will become clearer in Figs. 2 and 3 below), and is called θw or θweak. Through the action of the Higgs field on the particles, this one number determines many things, including

• the relative masses of the W and Z bosons
• the relative lifetimes of the W and Z bosons
• the relative probabilities for Z bosons to decay to one type of particle versus another
• the relative rates to produce different types of particles in scattering of electrons and positrons at very high energies
• the relative rates for processes involving scattering neutrinos off atoms at very low energies
• asymmetries in weak nuclear processes (ones that would be symmetric in corresponding electromagnetic processes)

and many others.

This is an enormously ambitious claim! When I began my graduate studies in 1988, we didn’t know if all these predictions would work out. But as the data from experiments came in during the 1990s and beyond, it became clear that every single one of them matched the data quite well. There were — and still are — no exceptions. And that’s why particle physicists became convinced that the Standard Model’s equations are by far the best they’ve ever found.

As an illustration, Fig. 1 shows, as a function of sin θw, the probabilities for Z bosons to decay to each type of particle and its anti-particle. Each individual probability is indicated by the size of the gap between one line and the line above. The total probability always adds up to 1, but the individual probabilities depend on the value of θw. (For instance, the width of the gap marked “muon” indicates the probability for a Z to decay to a muon and an anti-muon; it is about 5% at sin θw = 0, about 3% at sin θw = 1/2, and over 15% at sin θw = 1.)

Figure 1: In the Standard Model, once sin θw is known, the probabilities for a Z boson to decay to other particles and their anti-particles are predicted by the sizes of the gaps at that value of sin θw. Other measurements (see Fig. 3) imply sin θw is approximately 1/2 , and thus predict the Z decay probabilities to be those found in the green window. As Fig. 5 will show, data agrees with these predictions.

As we’ll see in Fig. 3, the W and Z boson masses imply (if the Standard Model is valid) that sin θw is about 1/2. Using that measurement, we can then predict that all the various decay probabilities should be given within the green rectangle (if the Standard Model is valid). These predictions, made in the mid-1980s, proved correct in the 1990s; see Fig. 5 below.

This is what I’ll sketch in today’s post. In future posts I’ll go further, showing how this works with high precision.

The Most Important Angle in Particle Physics

Angles are a common feature of geometry and nature: 90 degree angles of right-angle triangles, the 60 degree angles of equilateral triangles, the 104.5 degree angle between the two hydrogen-oxygen bonds in a water molecule, and so many more. But some angles, more abstract, turn out to be even more important. Today I’ll tell you about θw , which is a shade less than 30 degrees (π/6 radians).

Note: This angle is often called “the Weinberg angle”, based on Steven Weinberg’s 1967 version of the Standard Model, but it should be called the “weak-mixing angle”, as it was first introduced seven years earlier by Sheldon Glashow, before the idea of the Higgs field.

This is the angle that lies at the heart of the Standard Model: the smallest angle of the right-angle triangle shown in Fig. 2. Two of its sides represent the strengths g1 and g2 of two of nature’s elementary forces: the weak-hypercharge force and the weak-isospin force. According to the Standard Model, the machinations of the Higgs field transform them into more familar forces: the electromagnetic force and the weak nuclear force. (The Standard Model is often charaterized by the code SU(3)xSU(2)xU(1); weak-isospin and weak-hypercharge are the SU(2) and U(1) parts, while SU(3) gives us the strong nuclear force).

Figure 2: The electroweak right-triangle, showing the angle θw. The lengths of two of its sides are proprtional to the strengths g1 and g2 of the “U(1)” weak-hypercharge force and the “SU(2)” weak-isospin force.

To keep things especially simple today, let’s just say θw = 30 degrees, so that sin θw = 1/2. In a later post, we’ll see the angle is closer to 28.7 degrees, and this makes a difference when we’re being precise.

The Magic Angle and the W and Z Bosons

The Higgs field gives masses to the W and Z bosons, and the structure of the Standard Model predicts a very simple relation, given by the electroweak triangle as shown at the top of Fig. 3:

This has the consequence shown at the top of Fig. 3, rewritten as a prediction

If sin θw = 1/2 , this quantity is predicted to be 1/4 = 0.250. Measurements (mW = 80.4 GeV/c2 and mZ = 91.2 GeV/c2) show it to be 0.223. Agreement isn’t perfect, indicating that the angle isn’t exactly 30 degrees. But it is close enough for today’s post.

Where does this formula for the W and Z masses come from? Click here for details:

Central to the Standard Model is the so-called “Higgs field”, which has been switched on since very early in the Big Bang. The Higgs field is responsible for the masses of all the known elementary particles, but in general, though we understand why the masses aren’t zero, we can’t predict their values. However, there’s one interesting exception. The ratio of the W and Z bosons’ masses is predicted.

Before the Higgs field switched on, here’s how the weak-isospin and weak-hypercharge forces were organized: there were

• 3 weak isospin fields, called W+, W– and W0, whose particles (of the same names) had zero rest mass
• 1 weak-hypercharge field, usually called, X, whose particle (of the same name) had zero rest mass

After the Higgs field switched on by an amount v, however, these four fields were reorganized, leaving

• One, called the electromagnetic field, with particles called “photons” with zero rest mass.
• One, called Z0 or just Z, now has particles (of the same names) with rest mass mZ
• Two, still called W+ and W– , have particles (of the same names) with rest mass mW

Central to this story is θw. In particular, the relationship between the photon and Z and the original W0 and X involves this angle. The picture below depicts this relation, given also as an equation

Figure 3: A photon is mostly an X with a small amount of W0, while a Z is mostly a W0 with a small amount of X. The proportions are determined by θw .

The W+ and W– bosons get their masses through their interaction, via the weak-isospin force, with the Higgs field. The Z boson gets its mass in a similar way, but because the Z is a mixture of W0 and X, both the weak-isospin and weak-hypercharge forces play a role. And thus mZ depends both on g1 and g2, while mW depends only on g2. Thus

where v is the “value” or strength of the switched-on Higgs field, and in the last step I have used the electroweak triangle of Fig. 2.

Figure 3: Predictions (*before accounting for small quantum corrections) in the Standard Model with sin θw = 1/2, compared with experiments. (Top) A simple prediction for the ratio of W and Z boson masses agrees quite well with experiment. (Bottom) The prediction for the ratio of W and Z boson lifetimes also agrees very well with experiment.

A slightly more complex relation relates the W boson’s lifetime tW and the Z boson’s lifetime tZ (this is the average time between when the particle is created and when it decays.) This is shown at the bottom of Fig. 3.

This is a slightly odd-looking formula; while 81 = 92 is a simple number, 86 is a weird one. Where does it come from? We’ll see in just a moment. In any case, as seen in Fig. 3, agreement between theoretical prediction and experiment is excellent.

If the Standard Model were wrong, there would be absolutely no reason for these two predictions to be even close. So this is a step in the right direction. But it is hardly the only one. Let’s check the detailed predictions in Figure 1.

W and Z Decay Probabilities

Here’s what the Standard Model has to say about how W and Z bosons can decay.

W Decays

In this earlier post, I explained that W– bosons can decay (oversimplifying slightly) in five ways:

• to an electron and a corresponding anti-neutrino
• to a muon and a corresponding anti-neutrino
• to a tau and a corresponding anti-neutrino
• to a down quark and an up anti-quark
• to a strange quark and a charm anti-quark

(A decay to a bottom quark and top anti-quark is forbidden by the rule of decreasing rest mass; the top quark’s rest mass is larger than the W’s, so no such decay can occur.)

These modes have simple probabilities, according to the Standard Model, and they don’t depend on sin θw (except through small quantum corrections which we’re ignoring here). The first three have probability 1/9. Moreover, remembering each quark comes in three varieties (called “colors”), each color of quark also occurs with probability 1/9. Altogether the predictions for the probabilities are as shown in Fig. 4, along with measurements, which agree well with the predictions. When quantum corrections (such as those discussed in this post, around its own Fig. 4) are included, agreement is much better; but that’s beyond today’s scope.

Figure 4: The W boson decay probabilities as predicted (*before accounting for small quantum corrections) by the Standard Model; these are independent of sin θw . The predictions agree well with experiment.

Because the W+ and W- are each others’ anti-particles, W+ decay probabilities are the same as those for W–, except with all particles switched with their anti-particles.

Z Decays

Unlike W decays, Z decays are complicated and depend on sin θw. If sin θw = 1/2, the Standard Model predicts that the probability for a Z boson to decay to a particle/anti-particle pair, where the particle has electric charge Q and weak-isospin-component T = +1 or -1 [technically, isospin’s third component, times 2], is proportional to

• 2 (Q/2-T)2 + 2(Q/2)2 = 2+2TQ+Q^2

where I used T2 = 1 in the final expression. The fact that this answer is built from a sum of two different terms, only one of which involves T (weak-isospin), is a sign of the Higgs field’s effects, which typically marry two different types of fields in the Standard Model, only one of which has weak-isospin, to create the more familiar ones.

This implies the relative decay probabilities (remembering quarks come in three “colors”) are

• For electrons, muons and taus (Q=-1, T=-1): 1
• For each of the three neutrinos (Q=0, T=1): 2
• For down-type quarks (Q=-1/3,T=-1) : 13/9 * 3 = 13/3
• For up-type quarks (Q=2/3,T=1): 10/9 * 3 = 10/3

These are shown at left in Fig. 5.

Figure 5: The Z boson decay probabilities as predicted (*before accounting for small quantum corrections) by the Standard Model at sin θw = 1/2 (see Fig. 1), and compared to experiment. The three neutrino decays cannot be measured separately, so only their sum is shown. Of the quarks, only the bottom and charm decays can be separately measured, so the others are greyed out. But the total decay to quarks can also be measured, meaning three of the five quark predictions can be checked directly.

The sum of all those numbers (remembering that there are three down-type quarks and three up-type quarks, but again top quarks can’t appear due to the rule of decreasing rest mass) is:

• 1 + 1 + 1 + 2 + 2 + 2 + 13/3 + 13/3 + 13/3 + 10/3 + 10/3 = 86/3.

And that’s where the 86 seen in the lifetime ratio (Fig. 3) comes from.

To get predictions for the actual decay probabilities (rather than just the relative probabilities), we should divide each relative probability by 86/3, so that the sum of all the probabilities together is 1. This gives us

• For electrons, muons and taus (Q=-1, I=-1): 3/86
• For each of the three neutrinos (Q=0, I=1): 6/86
• For down-type quarks (Q=-1/3,I=-1) : 13/86
• For up-type quarks (Q=2/3,I=1): 10/86

as shown on the right-hand side of Fig. 5; these are the same as those of Fig. 1 at sin θw = 1/2. Measured values are also shown in Fig. 5 for electrons, muons, taus, the combination of all three neutrinos, the bottom quark, the charm quark, and (implicitly) the sum of all five quarks. Again, they agree well with the predictions.

This is already pretty impressive. The Standard Model and its Higgs field predict that just a single angle links a mass ratio, a lifetime ratio, and the decay probabilities of the Z boson. If the Standard Model were significantly off base, some or all of the predictions would fail badly.

However, this is only the beginning. So if you’re not yet convinced, consider reading the bonus section below, which gives four additional classes of examples, or stay tune for the next post in this series, where we’ll look at how things improve with a more precise value of sin θw.

Bonus: Other Predictions of the Standard Model

Many other processes involving the weak nuclear force depend in some way on sin θw. Here are a few examples.

High-Energy Electron-Positron Collisions (click for details)

In this post I discussed the ratio of the rates for two important processes in collisions of electrons and positrons:

• electron + positron ⟶ any quark + its anti-quark
• electron + positron ⟶ muon + anti-muon

This ratio is simple at low energy (E << mZ c2), because it involves mainly electromagnetic effects, and thus depends only on the electric charges of the particles that can be produced.

Figure 6: The ratio of the rates for quark/anti-quark production versus muon/anti-muon production in high-energy electron-positron scattering depends on sin θw.

But at high energy (E >> mZ c2) , the prediction changes, because both electromagnetic and weak nuclear forces play a role. In fact, they “interfere”, meaning that one must combine their effects in a quantum way before calculating probabilities.

[What this cryptic quantum verbiage really means is this. At low energy, if Sf is the complex number representing the effect of the photon field on this process, then the rate for the process is |Sf|2. But here we have to include both Sf and SZ, where the latter is the effect of the Z field. The total rate is not |Sf|2 + |SZ|2 , a sum of two separate probabilities. Instead it is |Sf+SZ|2 , which could be larger or smaller than |Sf|2 + |SZ|2 — a sign of interference.]

In the Standard Model, the answer depends on sin θw. The LEP 2 collider measured this ratio at energies up to 209 GeV, well above mZ c2. If we assume sin θw is approximately 1/2, data agrees with predictions. [In fact, the ratio can be calculated as a function of energy, and thus made more precise; data agrees with these more precise predictions, too.]

Low-Energy Neutrino-Nucleus Collisions (click for details)

When electrons scatter off protons and neutrons, they do so via the electromagnetic force. For electron-proton collisions, this is not surprising, since both protons and electrons carry electric charge. But it’s also true for neutrons, because even though the neutron is electrically neutral, the quarks inside it are not.

By contrast, neutrinos are electrically neutral, and so they will only scatter off protons and neutrons (and their quarks) through the weak nuclear force. More precisely, they do so through the W and Z fields (via so-called “virtual W and Z particles” [which aren’t particles.]) Oversimplifying, if one can

• obtain beams of muon neutrinos, and
• scatter them off deuterons (nuclei of heavy hydrogen, which have one proton and one neutron), or off something that similarly has equal numbers of protons and neutrons,

then simple predictions can be made for the two processes shown at the top of Fig. 7, in which the nucleus shatters (turning into multiple “hadrons” [particles made from quarks, antiquarks and gluons]) and either a neutrino or a muon emerges from the collision. (The latter can be directly observed; the former can be inferred from the non-appearance of any muon.) Analogous predictions can be made for the anti-neutrino beams, as shown at the bottom of Fig. 7.

Figure 7: The ratios of the rates for these four neutrino/deuteron or anti-neutrino/deuteron scattering processes depend only on sin θw in the Standard Model.

The ratios of these four processes are predicted to depend, in a certain approximation, only on sin θw. Data agrees with these predictions for sin θw approximately 1/2.

More complex and detailed predictions are also possible, and these work too.

Asymmetries in Electron-Positron Collisions (click for details)

There are a number of asymmetric effects that come from the fact that the weak nuclear force is

• not “parity-invariant”, (i.e. not the same when viewed in a mirror), and
• not “charge-conjugation invariant” (i.e. not the same when all electric charges are flipped)

though it is almost symmetric under doing both, i.e. putting the world in a mirror and flipping electric charge. No such asymmetries are seen in electromagnetism, which is symmetric under both parity and charge-conjugation separately. But when the weak interactions play a role, asymmetries appear, and they all depend, yet again, on sin θw.

Two classes of asymmetries of great interest are:

• “Left-Right Asymmetry” (Fig. 8): The rate for electron-positron collisions to make Z bosons in collisions with positrons depends on which way the electrons are “spinning” (i.e. whether they carry angular momentum along or opposite to their direction of motion.)
• “Forward-Backward Asymmetry” (Fig. 9): The rate for electron-positron collisions to make particle-antiparticle pairs depends on whether the particles are moving roughly in the same direction as the electrons or in the same direction as the positrons.

Figure 8: The left-right asymmetry for Z boson production, whereby electrons “polarized” to spin one way do not produce Z’s at the same rate as electrons polarized the other way. Figure 9: The forward-backward asymmetry for bottom quark production; the rate for the process at left is not the same as the rate for the process at right, due to the weak nuclear force.

As with the high-energy electron-positron scattering discussed above, interference between effects of the electromagnetic and Z fields, and the Z boson’s mass, causes these asymmetries to change with energy. They are particularly simple, though, both when E = mZ c2 and when E >> mZ c2.

A number of these asymmetries are measurable. Measurements of the left-right asymmetry was made at the Stanford Linear Accelerator Center (SLAC) at their Linear Collider (SLC), while I was a graduate student there. Meanwhile, measurements of the forward-backward asymmetries were made at LEP and LEP 2. All of these measurements agreed well with the Standard Model’s predictions.

A Host of Processes at the Large Hadron Collider (click for details)

Fig. 10 shows predictions (gray bands) for total rates of over seventy processes in the proton-proton collisions at the Large Hadron Collider. Also shown are measurements (colored squares) made at the CMS experiment . (A similar plot is available from the ATLAS experiment.) Many of these predictions, which are complicated as they must account for the proton’s internal structure, depend on sin θw .

Figure 10: Rates for the production of various particles at the Large Hadron Collider, as measured by the CMS detector collaboration. Grey bands are theoretical predictions; color bands are experimental measurements, with experimental uncertainties shown as vertical bars; colored bars with hatching above are upper limits for cases where the process has not yet been observed. (In many cases, agreement is so close that the grey bands are hard to see.)

While minor discrepancies between data and theory appear, they are of the sort that one would expect in a large number of experimental measurements. Despite the rates varying by more than a billion from most common to least common, there is not a single major discrepancy between prediction and data.

Many more measurements than just these seventy are performed at the Large Hadron Collider, not least because there are many more details in a process than just its total rate.

A Fortress

What I’ve shown you today is just a first step, and one can do better. When we look closely, especially at certain asymmetries described in the bonus section, we see that sin θw = 1/2 (i.e. θw = 30 degrees) isn’t a good enough approximation. (In particular, if sin θw were exactly 1/2, then the left-right asymmetry in Z production would be zero, and the forward-backward asymmetry for muon and tau production would also be zero. That rough prediction isn’t true; the asymmetries are small, only about 15%, but they are clearly not zero.)

So to really be convinced of the Standard Model’s validity, we need to be more precise about what sin θw is. That’s what we’ll do next time.

Nevertheless, you can already see that the Standard Model, with its Higgs field and its special triangle, works exceedingly well in predicting how particles behave in a wide range of circumstances. Over the past few decades, as it has passed one experimental test after another, it has become a fortress, extremely difficult to shake and virtually impossible to imagine tearing down. We know it can’t be the full story because there are so many questions it doesn’t answer or address. Someday it will fail, or at least require additions. But within its sphere of influence, it rules more powerfully than any theoretical idea known to our species.

Amid all the shocking and depressing news regarding the future of American healthcare and medicine, at least over the next four years, I thought I would tackle something a bit lighter today. What happens to the brains of astronauts aboard the ISS? Space medicine is a field of study, if fairly niche, and will likely have increasing implications as humanity increases its […]

The post Your Brain In Space first appeared on Science-Based Medicine.

Many restaurants in countries such as England and the US now print calories on their menus, but some researchers question whether this is really tackling their obesity problem

The best pictures we have of the sun yet have been delivered thanks to the Solar Orbiter spacecraft

The effects of being in space can worsen an astronaut's working memory, processing speed and attention - which could be a problem for future missions

SpaceX’s Starship launch system went through its sixth flight test today, and although the Super Heavy booster missed out on being caught back at its launch pad, the mission checked off a key test objective with President-elect Donald Trump in the audience.

Trump attended the launch at SpaceX’s Starbase complex in the company of SpaceX CEO Elon Musk, who has been serving as a close adviser to the once and future president over the past few months. In a pre-launch posting to his Truth Social media platform, Trump wished good luck to “Elon Musk and the Great Patriots involved in this incredible project.”

President Trump has arrived to watch the SpaceX launch with @elonmusk! ? pic.twitter.com/D5awPUUQTC

— Trump War Room (@TrumpWarRoom) November 19, 2024

Starship is the world’s most powerful rocket, with 33 methane-fueled Raptor engines providing more than 16 million pounds of thrust at liftoff. That’s twice the power of the Saturn V rocket that sent Americans to the moon in the 1960s and early ’70s. The two-stage rocket stands 121 meters (397 feet) tall, with a 9-meter-wide (30-foot-wide) fairing.

Super Heavy had an on-time launch at 4 p.m. CT (22:00 UTC) and was set up to fly itself back to the launch tower to be caught by the giant “Mechazilla” arms that were successfully used during last month’s flight test. But four minutes after liftoff, mission controllers said the booster had to be diverted instead to make a soft splashdown in the Gulf of Mexico. SpaceX didn’t immediately report the reason for the diversion.

“It was not guaranteed that we would be able to make a tower catch today,” launch commentator Kate Tice said during today’s webcast. “So, while we were hoping for it … the safety of the teams and the public and the pad itself are paramount. We are accepting no compromises in any of those areas.”

While the booster settled majestically into the Gulf, the Starship second stage — known as Ship for short — continued on a track that sent it as high as 190 kilometers (120 miles). A plush banana was placed in Ship’s cargo bay as a zero-gravity indicator, and Tice wore a T-shirt bearing the words “It’s Bananas!” to play off the lighthearted theme.

Ship successfully relit one of its methane-fueled Merlin engines while in space, which was a key objective for today’s suborbital test. Relighting the engines under such conditions will be required in the future for Ship’s orbital maneuvers.

A little more than an hour after launch, Ship’s engines fired for a final time to make a controlled splashdown in the Indian Ocean. The daylight visuals, plus other data collected during the flight, will help SpaceX’s team fine-tune Starship’s design for future tests.

SpaceX plans to use Starship to accelerate deployment of its Starlink broadband satellites, as well as to fly missions beyond Earth orbit. The company has a $2.9 billion contract from NASA to provide a version of Starship that’s customized for lunar landings, starting as early 2026. And Musk has said Starship could take on uncrewed missions starting that same year — with the first crewed mission set for launch in 2028 if everything goes right.

NASA Administrator Bill Nelson referred to those future flights in a message on Musk’s X social-media platform:

Congrats to @SpaceX on Starship's sixth test flight. Exciting to see the Raptor engine restart in space—major progress towards orbital flight.

Starship’s success is #Artemis’ success. Together, we will return humanity to the Moon & set our sights on Mars. pic.twitter.com/tuwpGOvT9S

— Bill Nelson (@SenBillNelson) November 19, 2024

Check out these other postings tracking the progress of the flight test:

With data and flight learnings as our primary payload, Starship’s sixth flight test once again delivered ? https://t.co/oIFc3u9laE pic.twitter.com/O6ZKThQRr6

— SpaceX (@SpaceX) November 20, 2024

Super Heavy initiates its landing burn and softly splashes down in the Gulf of Mexico pic.twitter.com/BZ3Az4GssC

— SpaceX (@SpaceX) November 19, 2024

Starship’s Raptor engine burn is complete and Starship has entered a coast phase pic.twitter.com/xJHlg2eDTs

— SpaceX (@SpaceX) November 19, 2024

Live views of Earth from Starship pic.twitter.com/3rgsHSj2km

— SpaceX (@SpaceX) November 19, 2024

Starship preparing to splash down in the Indian Ocean pic.twitter.com/EN9jibr07l

— SpaceX (@SpaceX) November 19, 2024

Splashdown confirmed! Congratulations to the entire SpaceX team on an exciting sixth flight test of Starship! pic.twitter.com/bf98Va9qmL

— SpaceX (@SpaceX) November 19, 2024

The post Starship’s Booster (and Donald Trump) Make a Splash With Sixth Flight Test appeared first on Universe Today.

Analysis of millions of galaxies upholds Albert Einstein’s ideas about gravity and also offers tantalising new hints of how dark energy may have evolved

Energy stored in thermochemical materials can effectively heat indoor spaces, particularly in humid regions, according to researchers.

Astronomers have discovered the first pairs of white dwarf and main sequence stars -- 'dead' remnants and 'living' stars -- in young star clusters. This breakthrough offers new insights on an extreme phase of stellar evolution, and one of the biggest mysteries in astrophysics.

Elon Musk’s SpaceX is preparing for the sixth test flight of Starship, the world's most powerful rocket. It aims to conduct the launch at 4pm Central Time (10pm UK). Here’s everything we know so far

Thanks to the Hubble Space Telescope, we all have a vivid image of the Crab Nebula emblazoned in our mind’s eyes. It’s the remnant of a supernova explosion Chinese astronomers recorded in 1056. However, the Crab Nebula is more than just a nebula; it’s also a pulsar.

The Crab Pulsar pulsates in an unusual ‘zebra’ pattern, and an astrophysicist at the University of Kansas thinks he’s figured out why.

When massive stars explode as supernovae, they leave behind remnants: either a stellar-mass black hole or a neutron star. SN 1054 left behind the latter. The neutron star is highly magnetized and spins rapidly, emitting beams of electromagnetic radiation from its poles. As it spins, the radiation is intermittently directed towards Earth, making it visible to us. In this case, it’s called a pulsar.

Pulsars are complex objects. They’re extremely dense and can pack up to three solar masses of material into a sphere as small as 30 km in diameter. Their magnetic fields are millions of times stronger than Earth’s, they can rotate hundreds of times per second, and their immense gravity warps space-time. And their cores are basically huge atomic nuclei.

One result of their complexity is their radio emissions, and this is especially true of the Crab Pulsar.

Pulsars are known for their main pulse (MP), but they also emit other pulses that are more difficult to detect. In 2007, radio astronomers Hankins and Eilek discovered a strange pattern in the Crab Pulsar’s high-frequency radio emissions. This is the only pulsar known to produce these patterns between the pulsar’s main pulse (MP) and its intermittent pulse (IP).

“The mean profile of this star is dominated by a main pulse (MP) and an interpulse (IP),” Eilek and Hankins wrote in their paper. However, there are two additional pulses called HFC1 and HFC2 that create the zebra pattern.

This figure shows the mean profile of the Crab pulsar over a wide range of frequencies. The MP and IP are shown by dashed lines at pulse phases 70° and 215°. However, between 4.7 and 8.4 GHz, the IP is offset from the IP at lower and higher frequencies. This constitutes the Crab Pulsar’s ‘zebra’ pattern. Two new high-frequency components also appear (labelled HFC1 and HFC2). Image Credit: Moffett & Hankins 1996.

Nobody has succeeded in explaining this unusual pattern. However, new research published in Physical Review Letters may finally explain it. The author is Mikhail Medvedev, who specializes in Theoretical Astrophysics at the University of Kansas. His research is “Origin of Spectral Bands in the Crab Pulsar Radio Emission.”

Medvedev says that the Crab Pulsar’s plasma-filled magnetosphere acts as a diffraction screen to produce the zebra pattern. This can explain the band spacing, the high polarization, the constant position angle, and other characteristics of the emissions.

This figure shows the overall geometry of the crab pulsar system. The red star is the pulsar. Its emissions pass through the plasma-filled magnetosphere, which acts as a diffraction screen, producing the zebra pattern of pulses. Image Credit: Medvedev 2024.

A typical pulsar emits radio emissions from its poles, as shown in the figure below. They sometimes emit two signals per rotation period, one radio and one high frequency. They appear in a different phase of the rotation, with the higher frequency emission produced outside the light cylinder, the region where linear speed approaches the speed of light.

This figure shows how a standard pulsar emits radio emissions. Electrons and positrons are accelerated through one of the gaps in the magnetosphere. They stream along the open magnetic field lines and emit coherent radio emissions from the poles. Image Credit: National Radio Astronomy Observatory.

But the Crab Pulsar is different.

“The Crab pulsar is, in contrast, very special. Its radio main pulse and interpulse are coincident in phase with high-energy emission, indicating the same emission region,” Medvedev explains.

Medvedev explains that the High-Frequency Interpulse (HFIP) produced by the diffraction effect creates the zebra pattern. “The spectral pattern of the high-frequency interpulse (HFIP), observed between about
?~5 and ?~30 GHz is remarkably different and represents a sequence of emission bands resembling the
“zebra” pattern,” he writes.

This simple schematic helps explain the diffraction effect. The different colours represent different densities in the plasma field. Regions of the magnetosphere with different densities either co-rotate with the pulsar or not, helping create the zebra pattern in the emissions. Image Credit: Medvedev 2024.

Medvedev’s proposed model has an additional benefit. He says it can be used to perform tomography on pulsars to uncover more details about their powerful magnetospheres.

“The model allows one to perform “tomography” of the pulsar magnetosphere,” he writes.

“We predict that this HFIP properties can also be observed in other pulsars if their radio and high energy emission are in phase. This would happen if the radio emission is produced in the outer magnetosphere as opposed to the “normal” emission from the polar region,” Medvedev explains.

This composite image of the Crab Nebula features X-rays from Chandra (blue and white), optical data from Hubble (purple), and infrared data from Spitzer (pink). Chandra has repeatedly observed the Crab since the telescope was launched into space in 1999. Image Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech

Medvedev says his model can also explain the HFC1 and HFC2 in the Crab Pulsar’s emissions spectrum. They’re also artifacts of his proposed diffraction model. “We propose that these high-frequency components are the reflections off the magnetosphere of the same source producing the diffracted HFIP,” he explains.

“To conclude, we propose a model, which explains the peculiar spectral band structure (the zebra pattern) of the high-frequency interpulse of the Crab pulsar radio emission,” Medvedev writes.

The post The Strange Pulsar at the Center of the Crab Nebula appeared first on Universe Today.

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