The effects on the solar system of having a few solar mass black hole cruise by within 65ly (or less than that for a neutron star) are exactly the same as having a normal star of the same mass do so. And there are plenty of them already within 65ly.

The one way a compact object differs is that if there's a companion star dumping gas into it, you get X-rays. But these are a) much more rare; b) not in the "invisible" population being discussed in this paper, and c) I suspect you'd still have to be either pretty close to one (and/or lined up exactly wrong in a jet) to care.

Any shaped star getting way closer than any current star might perturb the Oort cloud and shovel more comets into the inner solar system: this has been proposed for some of the mass extinction events. Don't need a compact object for that, though.

Actually, it's just coming back up after an upgrade, and is now in "Run 3". After each of Run 1 and Run 2 it was down for upgrades (in 2013-2015, and 2018-2022). So, not really been running for 14 years now, rather about half that time.

In other news: it's common for accelerators to not run during peak energy times (usually the summer). To save money and to take load off the grid. Fermilab's nearly always off in the summer for this reason (beam coming back in October). Also gives you a good chance to do maintenance and upgrades.

When I write up the annual report for an NSF grant, I must take the final, published pdf of any articles that were published with that grant's support and upload them to NSF. Go look at the NSF "Public Access Repository" for the complete collection of everyone who wrote something funded by NSF. That's a condition of getting money from the NSF, and if the original article is paywalled, the public can get it from the NSF. Maybe other agencies aren't that far ahead of the curve?

And not even talking about arXiv.org, where all the physics and astro plus many math and CS articles go as e-prints at the same time as they're submitted to the journals in the first place.

Of course, TFA about open access is paywalled so I can't see what the details are :)

Apparently simply because pets take fewer baths than humans. The pet bug juice is similar in concept to you slapping on some deet, but you'll wash yours off faster than fido.

Gaia is not taking pictures and doing things that are diffraction limited in the sense you're thinking of. If it were, its small mirrors would be limited to tenths of an arcsecond resolution. However, it is doing successful astrometric measurements down to handfuls of micro-arc seconds. How it does so is really cool: It spins and sprays light from two apertures at 90 degrees from each other, continuously clocks its CCD, and compares the signals as they walk across the CCD. The diffraction-limited point spread function is much larger than the pixels on the camera, but as that moves across the pixels they are able to fit the centroid to better precision than if it was Just a Mirror. You'd need a mirror 10,000x larger to just brute-force the angular resolution.

Here's a good article on how it works. So: no, the mirror is not the limiting factor in this observatory.

Gaia is incredibly useful despite the "old" tech. The magic of that mission is not in the size of the mirror: it is trying to measure stars in our own galaxy, not far away dim things across the observable universe. The magic is in the incredible precision of the astrometry it does: the mirror just has to be "good enough" to enable the rest of the instruments.

So many astronomical measurements are built on knowing the star's position and velocity. Gaia's whole mission is to measure those things with way better error bars than ever before: so all the downstream things now also have way better error bars. Often without even needing to go make new observations: take the ones you did a few years ago and re-crunch with Gaia data (and error bars) under the hood instead of whatever astrometry you used to be using: poof, better answers. Then the people who used your numbers in their calculation get better answers too, and so on down the road.

Ash is part of what comes out of the smokestacks. It's been being captured since 1907 to one degree or another. However it's not all of what causes problems, and what's left is still not pleasant. Go read that paper. a couple posts up.

Fun fact: the patent royalties from the invention of the electrostatic precipitation go to fund basic research, something my students and neutrino experiments have benefited from.

Air pollution. Far less due to emissions controls in the US vs, say India. But still a lot of damage. (not even going into the CO2 side of things here).

In fact, there's a huge difference even between coal and the natural gas plants that are rapidly replacing the coal plants. I happen to have a citation to this from Nature Sustainability. Similar arguments for nukes v coal, I just don't happen to have a handy paper to cite there.

Any good GPS receiver I've seen of late gets info from all available networks, including GLONASS. So, if US-based GPS is being jammed but GLONASS isn't, the Ukrainian equipment keeps ticking along happily. Especially so, I'd imagine, since they're using Russian tech anyway, which might primarily depend on GLONASS in the first place.

So: for the jamming to be effective, it would need to stomp on all the different constellations' spectra. Maybe it is. In which case it's also taking out their own troops' systems too.

Which brings up a different question. The US system used to have two modes, imprecise civilian and precise military modes, to cover just this sort of eventuality. It was big news when Clinton (I think that was the guy in charge at the time) opted to turn of the "fuzzing" for civilian receivers, which opened the door for all the cool GPS applications we all have now. Presumably in time of war it could be turned back on, though. GLONASS probably does the same thing. Maybe that's also happening? TFA is pretty short on actual details.

That is certainly what students think. It also turns out not to be true. If the goal is "learn stuff", but you haven't learned it yet: I'm pretty sure that you don't even know what you don't know.

It's also a bad feedback loop. In the case of my students, they'll cheat on the homework, because "it's just homework, why bother?" Then, since they skipped the "practice it" step, they're screwed on tests since they don't actually know how to go about solving the problems, so are strongly motivated to cheat to cover up the fact that they haven't learned what they're supposed to have by that point. (and then it becomes my fault for writing a test that's "too hard!!!")

I teach physics: a random engineering student might indeed never end up needing "useless" information about electromagnetism, for example: but the real value comes in being able to approach a complicated problem and figure out how to solve it: a skill which is at the core of any future engineering job. So, not bothering with actually doing the useless homework: that student is completely missing the point as to why they're there in the first place.