Science

In 1936 astronomers watched as FU Orionis, a dim star in the Orion constellation, brightened dramatically. The star’s brightness increased by a factor of 100 in a matter of months. When it peaked, it was 100 times more luminous than our Sun.

Astronomers had never observed a young star brightening like this.

Since then, we’ve learned that FU Orionis is a binary star. It’s surrounded by a circumstellar disk and the brightness episodes are triggered when the star accretes mass from the disk. There are other young stars similar to FU Orionis, and it’s now the namesake for an entire class of variable young stars that brighten in the same manner. FU Ori stars are a sub-class of T-Tauri stars, young, pre-main sequence stars that are still growing.

Astronomers have modelled FU Ori’s accretion and brightness episodes with some success. But the nature of the disk-star interface has remained a mystery. Attempts to image the boundary between the two haven’t been successful. Until now.

Astronomers used the Hubble Space Telescope to observe FU Ori with the telescope’s COS (Cosmic Origins Spectrograph) and STIS (Space Telescope Imaging Spectrograph) instruments. Their results are published in The Astrophysical Journal Letters. The research is “A Far-ultraviolet-detected Accretion Shock at the Star–Disk Boundary of FU Ori” and the lead author is Adolfo Carvalho. Carvalho is an Astronomy PhD candidate at Caltech.

FU Ori stars are T-Tauri stars that represent the most actively accreting young stellar objects (YSOs). The outward magnetic pressure from T-Tauri stars prevents the disk from touching the star. Astronomers think that classical T-Tauri stars accrete material along their magnetic field lines and deposit on the poles in a process called magnetospheric accretion.

This schematic shows how magnetospheric accretion works on T-Tauri stars. Image Credit: Adapted from Hartmann et al. (2016).

However, FU Ori stars are different. They’ve undergone disk instability either because the disk is so much larger than the star, because of the presence of a binary, or from infalling material. The instability leads to rapid changes in the accretion rate. The increased rate of accretion upsets the balance between the star’s magnetic field and the inner edge of the accretion disk. The spectra of FU Ori stars is dominated by absorption features from the inner disk. Excess emissions from those stars is understood as matter shocking onto the star’s photosphere. However, for FU Ori stars, astronomers are uncertain about the detailed structure of the accretion boundary layer.

The researchers focused on the inner edge of FU Ori’s accretion disk in an attempt to confirm the accretion disk model and understand the boundary layer more completely.

“We were hoping to validate the hottest part of the accretion disk model, to determine its maximum temperature, by measuring closer to the inner edge of the accretion disk than ever before,” said Lynne Hillenbrand of Caltech in Pasadena, California, a co-author of the paper. “I think there was some hope that we would see something extra, like the interface between the star and its disk, but we were certainly not expecting it. The fact we saw so much extra — it was much brighter in the ultraviolet than we predicted — that was the big surprise.”

In FU Ori stars, the accretion disk is closer than in T-Tauri stars. This, combined with the enhanced infall rate, makes them much brighter than T-Tauris. In fact, during an outburst, the disk actually outshines the star. The disk is orbiting faster than the star rotates, and this means there should be a region where the disk impacts the star. The impact slows the material down and heats it up.

This artist’s image helps illustrate FU Ori’s accretion and flaring. Left panel: Material from the dusty and gas-rich disk (orange) plus hot gas (blue) mildly flows onto the star, creating a hot spot. Middle panel: The outburst begins – the inner disk is heated, more material flows to the star, and the disk creeps inward. Right panel: The outburst is in full throttle, with the inner disk contacting the star. Image Credit: Caltech/T. Pyle (IPAC)

The new Hubble UV observations show that the region is there and that it’s much hotter than thought.

“The Hubble data indicates a much hotter impact region than models have previously predicted,” said lead author Carvalho. “In FU Ori, the temperature is 16,000 kelvins [nearly three times our Sun’s surface temperature]. That sizzling temperature is almost twice the amount prior models have calculated. It challenges and encourages us to think of how such a jump in temperature can be explained.”

That means that the scientific model of FU Ori stars, called the viscous disk accretion model, needs to be updated. The team’s revised model says that as material from the accretion disk approaches the star and reaches its surface, it produces a hot shock that emits ultraviolet light. The temperature of the shock suggests that the material is moving at 40 km/s at the boundary, which is in line with simulations of the accretion process.

“The measured temperature and the size of the FUV emission region are consistent with expectations for a shock at the disk–star boundary,” the authors explain in their research. “The shock arises from the collision of the highly supersonic disk surface accretion flow with the stellar photosphere.”

One question scientists have concerns exoplanet formation around young stars. Researchers think that planets start to form when stars are very young. Is this hot flaring a detriment to planet formation? Does it affect their evolution? The extreme UV accretion flaring that FU Ori stars undergo could affect the chemistry of planets.

“Our revised model based on the Hubble data is not strictly bad news for planet evolution, it’s sort of a mixed bag,” explained Carvalho. “If the planet is far out in the disk as it’s forming, outbursts from an FU Ori object should influence what kind of chemicals the planet will ultimately inherit. But if a forming planet is very close to the star, then it’s a slightly different story. Within a couple outbursts, any planets that are forming very close to the star can rapidly move inward and eventually merge with it. You could lose, or at least completely fry, rocky planets forming close to such a star.”

The post The Hubble and FU Orionis: a New Look at an Old Mystery appeared first on Universe Today.

Results showed that in almost all cases, measured bandwidths were higher than predictions by widely used models of the galaxy, highlighting a need for updates to current ISM density models.

Scientists around the world rely on ocean monitoring tools to measure the effects of climate change. Researchers advanced the technology available to measure carbon dioxide in the ocean.

Accelerating rates of heat uptake by oceans that don't fit current climate models can now be explained by quantum physics.

Researchers propose a new method to generate meteorological data that takes into account the interdependence of meteorological factors, such as temperature, humidity, and solar radiation.

Humans get a real buzz from the virtual world of gaming and augmented reality but now scientists have trialled the use of these new-age technologies on small animals, to test the reactions of tiny hoverflies and even crabs. In a bid to comprehend the aerodynamic powers of flying insects and other little-understood animal behaviors, the study is gaining new perspectives on how invertebrates respond to, interact with and navigate virtual 'worlds' created by advanced entertainment technology.

This unobtrusive, leaf-mounted sensor saves time and improves productivity by remotely monitoring the health of plants in real-time.

Creating and controlling quantum dots via electrical methods, is likely to lead to new frontiers in the quest to develop stable and efficient qubits. Exploring how zinc oxide can be used in electrically defined quantum dots, researchers have unearthed some surprising phenomenon.

Researchers have made a record-breaking astrophysical discovery while simultaneously uncovering a possible explanation for the rare and extreme astrophysical event known as long-period radio transients.

Dark ovals in Jupiter's polar haze, visible only at UV wavelengths, were first noticed 25 years ago, then ignored. A new study shows that these dark UV ovals are common, appearing at the south pole in 75% of Hubble Space Telescope images taken since 2015. They appear less often at the north pole. The scientists theorize that a magnetic vortex generated in the ionosphere stirs up and concentrates the hydrocarbon haze that blankets the poles.

Covalent organic framework compounds are more active as catalysts than one would expect. Researchers have now discovered why.

A new article examines the convergence of physics, chemistry, and AI, highlighted by recent Nobel Prizes. It traces the historical development of neural networks, emphasizing the role of interdisciplinary research in advancing AI. The authors advocate for nurturing AI-enabled polymaths to bridge the gap between theoretical advancements and practical applications, driving progress toward artificial general intelligence.

A chemical reaction can convert two polluting greenhouse gases into valuable building blocks for cleaner fuels and feedstocks, but the high temperature required for the reaction also deactivates the catalyst. A team has found a way to thwart deactivation. The strategy may apply broadly to other catalysts.

Engineers and biochemists have brought their skills together to make it possible for untrained users to confirm contamination in fluids using a biogel test that changes color in the presence of such bacteria as E. coli, listeria and other frequent testing targets.

Researchers share a mathematical model created to capture the nonlinear relationships between CO2, temperature, human population, and crop growth. Increasing evidence of chaotic and complex dynamics within ecological systems led them to use both autonomous and nonautonomous models to gain a deeper understanding of seasonal variations and potential mitigation strategies, such as developing temperature-tolerant crops.

Food in the US has a bad rap thanks to outbreaks caused by bacteria, plus processing, additives and food dyes, but the food supply is actually much less risky than people think

Today's huge AI models are composed of several billion numbers known as weights and changing just one of them can destroy their ability to function, leading to “gibberish” output

Inflatable space modules are not a new concept, NASA have been exploring the possibility since the 1960’s. The Chinese Space Agency is now getting in on the act and is testing its new inflatable module which is part of its Shijian-19 satellite launch. To get it into orbit the capsule was compressed and folded and then inflated once in orbit. Following completion of the tests, it re-entered the atmosphere, landing in the Gobi Desert on 10th October. The goal is for this to be used to extend its space station in the same way NASA have been exploring expansion of ISS. 

The idea of inflatable space capsules offers a lightweight solution which simplifies the launch process. Their development began back in the 1960’s but real progress was seen with projects like TransHub that looked at new advanced materials. Even though TransHub was cancelled it was a precursor to ventures like the Bigelow Aerospace module known as BEAM. It was tested in 2016 on the ISS and proved the concept could work making them an invaluable part of the future of space exploration. 

This computer rendering shows the Bigelow Expanded Activity Module in its fully expanded configuration. Image: NASA

The Chinese National Space Administration (CNSA) has now started experimentation with inflatable modules. They have been a major player on the global space stage since it was founded in 1993. Among their successes have been the Chang’e lunar missions and the Tianwen-1 Mars explorers. Since 2021, the Tiangong space station has been in orbit high above the Earth and there are now plans for crewed lunar missions. 

A recovery team member checks the Chang’e-6 probe’s sample return capsule after its landing in Inner Mongolia. (Credit: CGTN / CNSA)

On 27th September, the CNSA launched their Shijian-19 retrievable satellite from Jiuquan in China. A test inflatable module was developed and manufactured by the China Academy of Space Technology (CAST) as a landmark step in getting an inflatable module in orbit. They confirmed that the inflatable flexible sealed module completed a successful orbital test. The module is a sealed structure made from composite materials much like the Bigelow Aerospace BEAM module. 

Launch is completed by compressing and folding the module and then inflating upon reaching orbit. The technique makes construction relatively cheap and the launch process far more efficient. Following on from the successful test, CAST promise that larger-scale modules are the next step marking an important step forward in sealed module technology. To arrive at this stage in the development of inflatable technology, CAST completed ground based tests that confirmed they were air tight, could deal with extreme pressures and vibrations and would be capable of with standing impact from space debris. 

A rendering of the Chinese Tiangong space station. Credit: CMSA

The CNSA have confirmed they plan to expand their Tiangong space station and are now exploring the possibility of using inflatable modules as part of their plans. The next likely module to be added is likely to be a multifunctional capsule that will allow other modules to be added. The success of the inflatable module opens up a number of possibilities and opportunities for the Chinese agency, not just for Tiangong but for other space exploration habitats. 

Source : China’s inflatable space capsule passes in-orbit test

The post China Tests a Reusable Inflatable Module in Space appeared first on Universe Today.

I can guarantee that nearly everyone reading this post is using way too much toothpaste when they brush their teeth. In fact, you’re probably using at least four times the amount you need, and thus you’re paying four times what you should be paying for toothpaste. Not only that, but you may be getting too much fluoride if you are, like most people, using a fluoridated toothpaste. (RFK Jr. may get rid of those!)

How much toothpaste do you need? Several hygienists have told me “the amount about the size of a pea”, and I have verified that from several sites (for example, here, here, and here). Nobody weighs their toothpaste, but this amount is roughly 0.25 grams of paste. That means that a small three-ounce tube should last about six months if you brush twice a day.

And here are photos showing the proper amount of toothpaste to use for both small children and those more than three years old (that includes us):

Source

If you’re dispensing a ribbon of toothpaste that extends the length of the bristles, you’re using (and spending) way too much. STOP IT!

About 40 years ago, researchers noticed a population of orcas had begun swimming around with dead fish on their heads, and now the craze is back