Month: June 2024

Many people interested in astronomy know the Hyades and the Pleiades. They are star clusters in the constellation Taurus. They are two of a handful of star clusters that are visible to the naked eye in dark skies.

It turns out that these clusters, as well as more than 150 other clusters nearby, all originate from just three massive star-forming regions.

Open clusters such as the Hyades and Pleiades contain hundreds of stars loosely bound together by mutual gravity. They have fewer stars than globular clusters and are not as densely packed. They are also not spherical like globular clusters, but follow the galactic plane. They are usually found in the spiral arms of the Milky Way rather than in the halo where globular clusters are located.

Open star clusters eventually lose their gravitational bond with each other and are called stellar associations. They still move together through space and are then called a moving group. Their motion allows astronomers to understand their origins.

In a new research article in Nature, a team of researchers has traced the origins of 155 young star clusters within about 3,500 light years of the Sun. The article is titled “Most nearby young star clusters formed in three massive complexes.” The authors come from institutes in Austria, Germany and the USA.

“Young star clusters are ideal for studying the history and structure of the Milky Way. By studying their movements in the past and thus their origin, we also gain important insights into the formation and evolution of our galaxy,” says João Alves of the University of Vienna, co-author of the study.

The researchers used Gaia data and spectroscopic observations of star clusters to trace their history back 60 million years. They discovered three families of star clusters, each of which is associated with one of three star-forming regions. “This suggests that the young star clusters originate from only three very active and massive star-forming regions,” says Alves.

The researchers started with a sample of 272 star clusters. They found that between 30 and 50 million years ago, almost 60 percent of their orbits converged in three locations. This showed that “a large proportion of star clusters in the solar neighborhood have common origins.”

The three cluster families are named after their best-known members: Collinder 135 (Cr135), Messier 6 (M6), and Alpha Persei (?Per). The clusters contain 39, 34, and 82 star clusters, respectively. Together, they contain 57% of the 272 star clusters in the sample and 59% of the 48,514 stars in the sample.

This research illustration shows the positions of the clusters' stars across the sky, as well as some optical images of some of their members. Alpha Persei's members are spread out further across the sky because they are closest to the Sun. (Interactive version here.) Image credit: Swiggum et al. 2024.

“These findings provide a clearer understanding of how young star clusters in our galactic neighborhood are connected to each other, similar to family members or 'bloodlines,'” says lead author Cameron Swiggum, a doctoral student at the University of Vienna. “By studying the three-dimensional motions and past positions of these star clusters, we can identify their common origin and locate the regions in our galaxy where the first stars in these respective star clusters formed up to 40 million years ago.”

The team's research uncovered more than just the history of the star clusters. They also found that over 200 supernova explosions must have occurred in the three star-forming regions to eject all of these clusters. However, supernova explosions are extraordinarily powerful, and 200 of them release enough energy to shape their surroundings on a large scale.

The authors say these explosions created a gigantic bubble in the ISM. “This could explain the formation of a superbubble, a giant bubble of gas and dust 3,000 light-years in diameter around the Cr135 family,” Swiggum said in a press release.

Our solar system is also located in one of these bubbles, the Local Bubble. Inside the bubble, the gas is thinner and hotter than outside. “The Local Bubble is also probably linked to the history of one of the three star cluster families,” adds Swiggum. “And it has probably left traces on Earth, as measurements of iron isotopes (60Fe) in the Earth's crust suggest.”

This image from the research shows three star cluster families and other local features on a dust map. The dust is shown in gray and two prominent dust features, the Vela Molecular Ridge and the Radcliffe Wave, are labeled. The Sun is the yellow dot and the local bubble is shown in blue. (Interactive version here.) Image credit: Swiggum et al. 2024.

It's a truism that finding connections between things creates meaning. The stars in the sky aren't just “there.” There's a long story to tell when you unravel what we perceive as static. This research is another example of the powerful Gaia spacecraft's ability to find relationships between stars and weave an evidence-based story of their history. And we're somewhere in the middle of it.

“We can essentially turn the sky into a time machine that allows us to trace the history of our home galaxy,” says João Alves. “By deciphering the genealogy of star clusters, we can also learn more about our own galactic lineage.”

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By NOT MANY PEOPLE KNOW THAT

By Paul Homewood

The cost of manufacturing and installing electrolyzers for green hydrogen production in China, the US and Europe – three of the world's largest markets – has increased by more than 50 percent year-on-year, according to research institute BloombergNEF (BNEF). However, in its analysis, this had not led to a gradual reduction, as had previously been indicated.

The main culprit for Western manufacturers is inflation, which has driven up the cost of materials, utilities (such as water and electricity) and labor in the U.S. and Europe, BNEF said in its new report, “Electrolyser Price Survey 2024.”

As a result, the average system cost (including chimney and residual plant) for an electrolyzer made in China is now in the mid-range of US$600/kW, while machines made in Europe or the US cost around US$2,500/kW.

This makes Western electrolyzers four times more expensive than their Chinese counterparts, and this gap has not closed since the last report, BNEF noted.

The research institute had previously predicted that costs would gradually decline over a three-year period starting in 2022 as more and more major projects moved closer to completion.

https://www.hydrogeninsight.com/electrolysers/cost-of-electrolysers-for-green-hydrogen-production-is-rising-instead-of-falling-bnef/2-1-1607220

Green hydrogen, once touted as the savior of net-zero emissions, seems to have faded from the scene recently. A few years ago, there were wild, unproven predictions that hydrogen would be so cheap and easy to produce that we could all do without fossil fuels.

Instead, Bloomberg now reports, the costs of electrolyzers are rising instead of falling. In addition, the real costs of wind energy are much higher than previously thought, so green hydrogen is becoming significantly more expensive as a result.

So let’s take a closer look at these costs.

BEIS published this report back in 2018:

https://www.gov.uk/government/publications/hydrogen-supply-chain-evidence-base.

I analyzed the report here.

This table was included:

I expect PEM (Proton Exchange Membrane) technology to be the most likely to be adopted, with base cost in 2025 estimated at £500/kW.

A study last October put the average price at €727, or about £630 per kilowatt. Bloomberg puts it at $600, but that's based on extremely low Chinese production costs, which are almost certainly heavily subsidised. Tellingly, it's estimated that electrolysers made in Europe are four times as expensive.

We can therefore reasonably estimate costs to be in the region of £600.

The BEIS study assumed 52.0 kWh/kg H2 in 2025. However, the energy density of hydrogen is 33.3 Kwh per kg, which means that the electrolysis process only works at 64% efficiency. In other words, 36% of the energy used is lost.

Previous cost estimates were based on the lowest cost of renewables, in particular offshore wind, which would have to provide the majority of the electricity needed for electrolysis in the UK. As we now know, these costs were never realistic. The administrative strike price for offshore wind for AR6 is now £100/MWh at 2023 prices. Therefore, taking into account an energy efficiency of only 64%, the energy input cost of hydrogen is £156/MWh.

Then there are the running costs. BEIS calculated £21/MWh in 2018, which is now probably in the region of £30.

So we are already at £186/MWh, without adding in the capital costs. BEIS estimated this to be around £30/MWh in 2018, but this assumed a loan interest rate of 5%. Given the rise in interest rates since then and general inflation, a capital expenditure of £60/MWh is not unreasonable.

The total cost is therefore £246/MWh.

Wholesale natural gas prices have ranged from 55p to 85p per therm this year. The conversion rate is 29.3kWh per therm, giving a cost of £23.90 per MWh, based on a mean of 70p.

Does anyone still think hydrogen is a good idea?

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Related

To date, astronomers have confirmed the existence of 5,638 extrasolar planets in 4,199 star systems. In the process, scientists have discovered many worlds that have exceeded all expectations. This is certainly true of the “hot Neptunes,” planets that resemble the “ice giants” of the outer solar system but orbit much closer to their stars. However, when a team of astronomers led by Johns Hopkins University discovered TIC365102760 b (also known as Pheonix), they observed something completely unexpected: a planet the size of Neptune that maintained its atmosphere by puffing up.

Sam Grunblatt, an astrophysicist in JHU's William H. Miller III Department of Physics and Astronomy, led the research. He was joined by an international team that included Nicholas Saunders, NSF Graduate Research Fellow, Shreyas Vissapragada, Steven Giacalone, Ashley Chontos and Joseph M. Akana Murphy, 51 Pegasi b Fellows, and researchers from many prestigious institutes and universities. The paper describing their findings (which recently appeared in the Astrophysical Journal) is part of a series called “TESS Giants Transiting Giants.”

Artist's impression of JG436b, a hot Neptune located about 33 light-years from Earth. Image credit: STScI

Puff planets are a new class of incredibly rare exoplanets, estimated to make up 1% of all planets in our galaxy. The team discovered Pheonix by combining data from the Transiting Exoplanet Survey Satellite (TESS) with radial velocity measurements obtained by the High Resolution Echelle Spectrometer (HIRES) at the Keck Observatory. Their data showed that Pheonix is ​​0.55 times the size of Jupiter but only 0.06 times as massive, and orbits a red giant star with a period of 4.21285 days (about six times closer to its star than the distance between Mercury and the Sun).

Based on the age and temperature of its star, as well as the planet's remarkably low density, the team hypothesized that Phoenix's gaseous envelopes must have been separated billions of years ago. Based on its density, the team also estimates that the planet is the most bloated “puff planet” yet (about 60 times less dense than the densest “hot Neptune”) and that it will begin rotating into its star in about 100 million years. As Grunblatt explained in a JHU HUB press release:

“This planet is not evolving as we thought. It appears to have a much larger, less dense atmosphere than we expected for these systems. How it was able to retain this atmosphere despite being so close to such a large parent star is the big question.”

“It is the smallest planet we have ever found around one of these red giants, and probably the lowest-mass planet that has a [red] “The biggest star we've ever seen. That's why it looks really strange. We don't know why it still has an atmosphere, while other 'hot Neptunes', which are much smaller and denser, seem to lose their atmosphere in much less extreme environments.”

Artist's impression of Phoenix, the “hot Neptune” orbiting a red giant star 8 billion light-years from Earth. Image credit: Roberto Molar Candanosa/JHU

These findings could provide new insights into the late evolution of planetary systems and help scientists predict what will happen to the solar system in a few billion years. According to standard models of stellar evolution, our sun will exit its main sequence phase, expand into a red giant, and eventually engulf the inner planets. Based on these findings, they predict that Earth's atmosphere may not evolve as astronomers previously expected. Instead of our sun blasting it away, our atmosphere could expand and become incredibly “puffy.”

Pheonix is ​​the latest bloated planet that the international team has studied using TESS data. While bloated planets are considered rare, exoplanets like Pheonix are particularly difficult to find due to their small size and low density. In the future, Grunblatt and his colleagues plan to search for more of these smaller worlds and have already identified a dozen potential candidates by combining transit and radial velocity data.

Further reading: John Hopkins University, The Astrophysical Journal

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