Wrong: the belief that a red dwarf was not life-hostile + How big are neutron stars?

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Astronomers thought they'd found a red dwarf that wasn't hostile to its habitable zone planets -- they were wrong

EXCERPTS: M-type red dwarf stars have become a focus of exoplanet research because they appear to be the most likely place where rocky (aka. Earth-like) planets can be found orbiting within the star’s habitable zone (HZ). However, that does not mean that red dwarf stars are good candidates for hosting habitable planets. Take GJ 887, for example, one of the brightest M stars in the sky that has a system of two (possibly three) planets. In the past, this star was believed to be calm and stable, but new research by astronomers from Arizona State University has shown that GJ 887 might not be so calm as previously thought.

This is discouraging news since GJ 887 (aka. Lacaille 9352), which is located just under 11 light-years from Earth, was recently confirmed to have two Super-Earths whose orbits placed them close to or within the star’s HZ. Similar findings indicated that the star itself was relatively “boring,” meaning that it was not prone to flare-ups the way other red dwarf stars are – which was seen as good news as far as its habitability was concerned.

[...] These findings are also discouraging because they demonstrate once again that red dwarf stars, which are the most common star in the Universe (accounting for 75% of stars in the Milky Way alone) have a tendency to blast their planets with harmful radiation. Along with their tendency to host rocky planets, like Proxima b or TRAPPIST-1s seven planet system, this has made them a key part in humanity’s search for habitable exoplanets.

Beyond being prone to flare-ups, red dwarfs can also be deceptive in how they go about doing it. While they might appear calm in visible light (which was what GJ 887 showed) they can regularly emit flares that are only visible in other wavelengths. Since photons in the UV wavelength have much more energy than visible light, each flare will result in an orbiting planet being bombarded by fast-moving particles that could strip its atmosphere away... (MORE - details)

How big is a neutron star?

INTRO: Neutron stars are arguably the strangest objects in the cosmos. Born from the deaths of massive stars, they combine strong gravity with temperatures and densities higher than anything we can make in the lab. While we’ve known about neutron stars for the better part of a century, astrophysicists still aren’t entirely sure how large they are. That uncertainty is related to two other unanswered questions: What’s in the middle of neutron stars, and how massive can they grow?

We know they are comparatively tiny: Researchers estimate that a neutron star with a mass 1.4 times that of the sun will have a radius between 8 and 16 kilometers. The sun, by contrast, has a radius of about 433 thousand kilometers. Even ordinary stars are too small to be anything other than points of light in our most powerful telescopes, so direct measurement of the size of neutron stars is a hopeless case. However, astrophysicists are very good at indirect measurements... (MORE - details)

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