Month: June 2023

Hot Jupiters are large gaseous planets that orbit their star closely. Unlike our Jupiter, which radiates more heat than it receives from the Sun, hot Jupiters receive more heat from their star than from their interior. As a result, they can have a surface temperature of 1,000 K instead of the 160 K that Jupiter has. They are among the most common types of exoplanets and are the easiest type of exoplanets to discover.

Most hot Jupiters orbit red dwarf stars, which means they receive plenty of infrared light to keep them warm. But that also means they can easily radiate heat to maintain a constant temperature. One of the most common side effects of a hot Jupiter is that its upper atmosphere tends to swell and vaporize, creating either a fluffy, low-density world or a dense world devoid of lighter elements, depending on the stage.

There are some of these worlds that have extremely hot surfaces that make them appear star-like rather than planet-like. In 2017, astronomers discovered hot Jupiter KELT-9b. It orbits a bright blue star so closely that its period is only 1.5 days. This means that the planet is tidally connected to its star and starside temperatures reach more than 4,600 K. At that temperature, the molecules in its atmosphere would dissolve, creating a high-pressure region that would propel atoms to the dark side of the planet, where they would recombine into molecules. The surface temperatures of most stars in our galaxy are below those on the stellar side of the planet. KELT-9b was thought to be the exoplanet with the highest surface temperature, but a new world even hotter has recently been discovered.

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This new world orbits a star called WD 0032?317, which is not a main sequence star. It’s a white dwarf with a mass about half that of the Sun and a surface temperature of 37,000 K. That’s hot even for a white dwarf, meaning the star is likely to have crossed the main sequence less than left a million years ago. Its companion is a brown dwarf about 75 times the mass of Jupiter, so technically not a planet, but not a star either. It orbits the white dwarf so closely that its orbital period is only 2.5 hours.

The average temperatures of different exoplanets. Photo credit: Hallakoun et al

Calculating the surface temperature of this companion isn’t easy, but we know it must be very hot. White dwarfs emit light primarily in the ultraviolet range, while brown dwarfs emit primarily in the infrared. Therefore, it is much easier for the white dwarf to heat up the brown dwarf than it is for the brown dwarf to shed its thermal energy. Even a rough calculation gives a stellar temperature about as hot as the Sun.

In new work, the team used different models to determine an accurate surface temperature. The end result depends on whether the white dwarf has a core composed mostly of helium, or whether it has a core with a mixture of other elements, such as carbon. This would affect the amount of heat transferred to the brown dwarf. Based on their calculations, the brown dwarf star side likely has a surface temperature of around 8,000 K – 9,000 K. The dark side temperature is likely around 2,000 K. Compare this to the Sun’s surface temperature, which is around 5,700 K.

Reference: Hallakoun, Na’ama et al. “An irradiated analogue of Jupiter, hotter than the Sun.” arXiv preprint arXiv:2306.08672 (2023).

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The US has a long history of these types of anti-fossil fuel laws.

Here are some previous examples of these tactics from the US:

The continued use of lawfare by activists around the world when they fail through policy and legislation is now taking center stage in the UK.

The future of fossil fuels in the UK is in the spotlight this week, with the Horse Hill oil exploration case ending up in the Supreme Court on Wednesday. As the BBC reports, this is:

“A challenge that could mean the end of new fossil fuel projects in the UK.”

https://www.bbc.com/news/science-environment-65965119

This case is brought by a Surrey woman, Sarah Finch, who is challenging the legality of a local oil drilling permit.

The basis of the claim lies in the consideration of “downstream emissions” when approving building permits. As the BBC calls them:

“the greenhouse gas emissions released when the oil is used.”

https://www.bbc.com/news/science-environment-65965119

Finch argues that Surrey County Council failed to consider the impact of such emissions, which they estimate could amount to 10 million tonnes of carbon dioxide over a 20-year period.

In her argument, Finch draws an analogy, saying:

“Planning authorities say they don’t need to consider the climate impact of actually burning the oil – only the impact of drilling.” It’s like saying a chocolate cake is low in calories as long as you don’t eat it.”

https://www.bbc.com/news/science-environment-65965119

However, in a response from Surrey County Council, a spokesman stated:

“The District Council has a duty to decide planning applications in accordance with the Development Plan, the National Planning Framework, national policy and other relevant considerations as set out in legislation and case law.”

https://www.bbc.com/news/science-environment-65965119

You know, in democratic societies, politics is done quite normally.

As campaigners seek to halt all fossil fuel extraction, it is a legal strategy with national implications that extend beyond Surrey’s borders. Katie de Kauwe, an attorney for Friends of the Earth, noted:

“Developers are struggling with lawsuits like this because they are very concerned that when decision makers are confronted with the total carbon impact of these projects, which is the downstream emissions, they will reconsider giving them building permits.”

https://www.bbc.com/news/science-environment-65965119

When they fail to deny drilling permits nationally, these activists try to force local governments to comply.

The importance of the case is heightened by the involvement of outside groups, who have been asked by the court to provide additional evidence. These include West Cumbria Mining, a company that recently received permission to open the UK’s first new coal mine in 40 years. The Environmental Protection Agency also intervenes for the first time, stating that it is doing so because this is the case

“Wants legal clarity on how decision makers conduct environmental impact assessments when evaluating fossil fuel projects.”

https://www.bbc.com/news/science-environment-65965119

The Horse Hill case underscores the complexity of litigation in the power generation space. The outcome of this case could set an important precedent for how these projects will be evaluated and either given the green light or banned in the future.

A decision by the judges is expected to take three to six months.

HT/Rim

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When astronomers talk about the “end states” of stellar evolution, several categories come to mind: black holes, neutron stars/pulsars, and white dwarfs. What happens when a star lands in two of these states? Such is the case with a cross-genre white dwarf pulsar called J191213.72-441045.1 (J1912-4410 for short). It is part of a binary pair that includes a red dwarf star.

J1912-4410 is the size of Earth but the mass of the Sun. It’s also much cooler than the sun. It is surrounded by an incredibly strong magnetic field that contributes to its pulsar activity. It also rotates on its axis 300 times faster than Earth. In addition, it spits out some material every 5.5 minutes. This is what gives this white dwarf its “pulsar” appearance. But despite some of these properties, J1912-4410 is definitely not a neutron star. It behaves like a pulsar but looks like a white dwarf.

Understand J1912-4410

This newly discovered white dwarf pulsar is the second known object of its kind in the galaxy. The first, called AR Sco, was found in 2016 and is the prototypical white dwarf/M star pulsar. With a sample size of now two, astronomers can draw some useful conclusions about what drives them. These rapidly rotating, burned-out, highly magnetic stellar remnants illuminate their red dwarf companions with powerful beams of electrical particles and radiation. This causes the entire system to periodically lighten and fade dramatically. Why? Could the magnetic field play a role?

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According to Ingrid Pelisoli of the University of Warwick, it’s not clear what creates the enhanced magnetic field on a white dwarf pulsar. “The origin of magnetic fields is a big open question in many areas of astronomy, and that’s especially true for white dwarfs,” she said. “Magnetic fields in white dwarfs can be more than a million times stronger than the Sun’s magnetic field, and the dynamo model helps explain why.” The discovery of J1912-4410 was a crucial advance in the field.”

An artist’s rendering of crystallization in a white dwarf star. The two known white dwarf pulsars may have such interiors. Photo credit: Mark Garlick / University of Warwick.

White dwarf dynamos

The white dwarf dynamo model is an attempt to answer the question: How do white dwarfs get their magnetic fields? In general, white dwarfs have fields up to a million times stronger than Earth’s. Recent studies show that the engine that creates a magnetic field in a star is likely similar to the one that creates it inside our planet. Essentially, the movements of material within an object result in electrical currents that create the magnetic fields. In white dwarfs, however, it creates a much stronger field.

Astronomers believe that electric currents are caused by convection movements in the core of the white dwarf. These convection currents are caused by heat escaping from the solidifying core. Because a white dwarf is a cooling remnant of an aging star (like the Sun), its core will eventually “crystallize” as it cools. Because of their old age, the white dwarfs should be pretty cool in both the AR Sco and J1912-4410 systems. The temperature of J1912-4410 is low enough that such crystallization could (or will soon) take place. However, that doesn’t fully explain the activity these two white dwarf pulsars are showing, so they may not be quite at that stage yet.

Illustration of the origin of magnetic fields in white dwarfs in narrow binaries (read counter-clockwise). The magnetic field is created when a crystallizing white dwarf grows away from a companion star and as a result begins to spin rapidly. When the field of the white dwarf connects with the field of the secondary star, mass transport stops for a relatively short period of time. Author: Paula Zorzi

It turns out that the M-dwarf’s star companions also play a role in the action, Pelisoli said. “Their companions should be close enough that the white dwarf’s gravitational pull has historically been strong enough to capture mass from the companion, and this causes them to spin rapidly,” she noted. “All of these predictions apply to the newly found pulsar: the white dwarf is cooler than 13,000 K, spins on its axis every five minutes, and the white dwarf’s gravitational pull has a strong impact on the companion.”

Searching for candidates for the white dwarf pulsar

In a paper describing J1912-4410, Pelisoli and her team say that binary white dwarf pulsars pose a challenge to theoretical models describing white dwarfs. Basically, they wanted to understand why they are magnetically strong and bright across the spectrum. You ask: What is the nature of the dynamo that powers these strange animals? And what’s causing the emissions that make it look so “pulsar-like”?

They examined data from multiple surveys to find candidates similar to AR Sco. “After observing a few dozen candidates, we found one that had very similar light fluctuations to AR Sco,” Pelisoli said. “Our follow-up campaign with other telescopes revealed that this system was sending a radio and X-ray signal our way about every five minutes,” Pelisoli said. “This confirmed that there are more white dwarf pulsars out there, as predicted by previous models. There were other dynamo model predictions that were confirmed by the discovery of J1912-4410.”

After confirming that J1912-4410 was a white dwarf pulsar, the team asked if the “engine” (or dynamo) was the same as AR Sco’s. If it’s similar, that’s strong confirmation that the white dwarf dynamo model works.

More data required

There is still much to be done to understand these strange star beings and many questions to be answered. Does every white dwarf pulsar have exactly the same type of binary pair? Or are there subtle differences that contribute to the activity they show? At what point in its evolution is the white dwarf in such a pair? Does evolutionary level matter, especially given the white dwarf’s cooling temperature profile?

There are challenges. It is still difficult to determine the exact temperatures for white dwarf pulsars. In addition, the very periodic emission pulses that make these white dwarfs look like pulsars need to be studied more closely.

Finally, since the companions of these stellar oddities play a role in their pulsar-like activity, astronomers want to get a better idea of ​​their spectral types and orbits. Now that astronomers have two of these strange systems to study, they want to find more of them in our galaxy and beyond.

For more informations

The discovery of the white dwarf pulsar sheds light on stellar evolution
A pulsating white dwarf with a period of 5.3 minutes in a binary system detected from radio to X-rays
Discovered: The mechanism that creates giant white dwarf magnetic fields

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