We think that every big galaxy has a supermassive black hole in its center, with millions or even billions of times the mass of the Sun. In general, we also expect this monster to sit in the exact center of the galaxy. We call this the
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The spiral galaxy SDSS J043703.67+245606.8, seen here in a near-infrared Hubble Space Telescope image, has a central supermassive black hole that is moving with respect to the galaxy itself. Credit: NASA / ESA / STScI / Jenny Greene
But is it true everywhere? We know that smaller galaxies, with their correspondingly weaker gravity, can have offset black holes, but in those cases the black holes are generally underweight and easier to move around, possibly when the galaxy collides with another one. This can create gravitational havoc, moving the black hole off-center.
The cloud forms on the western flanks of the volcano Arsia Mons, the southernmost in a line of three ridiculously big volcanoes in an area of Mars called Tharsis, an enormous volcanic plateau about 5,000 km across (about the size of the continental United States). Arsia Mons is huge, about 500 km across and 17 km high. Mount Everest on Earth is only 9 km high, for comparison.
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Topography of the four huge volcanoes in the Tharsis region on Mars. All are hundreds of kilometers wide and have calderas 50 – 100 km wide. Arsia Mons is the farthest south, and is about 16 km high at the caldera. Credit: Hernández-Bernal et al., CC BY-SA 3.0 IGO license
Or, possibly, there’s a problem with how we’re observing it. Either way, something’s fishy.
In a nutshell, the Universe is expanding. There’s a whole bunch of different ways to measure that expansion. The good news is these methods all get
roughly the same number for it. The bad news is they don’t get
exactly the same number. One group of methods gets one number, and another group gets another number.
This discrepancy has been around awhile, and it’s not getting better. In fact, it’s getting worse (as astronomers like to say, there’s a growing tension between the methods). The big difference between the two groups is that one set of methods looks at relatively nearby things in the Universe, and the other looks at very distant ones. Either we’re doing something wrong, or the Universe is doing something different far away than it is near here.
They observed it for five years (from 2016 to 2020) with CARMENES (or Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle spectrographs, so you can see why they go with the acronym). This is a project to observe nearby red dwarfs (called M-type stars by astronomers) and look for Earth-sized planets orbiting them.
Two objects of different masses orbit each other; the more massive one makes a little circle and the lower mass one a bigger circle. Credit: NASA/Spaceplace
Astronomers found that the star underwent a shift with a 1.467-day period, indicating a planet in a close orbit. They found the planet has a mass of 2.8 times that of Earth, and orbits just 2.6 million kilometers from it. That’s
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What we see from an active galaxy depends in large part on our viewing geometry. If the jet is aimed at us we can see high-energy light like X-rays and gamma rays. If we see the dust torus edge-on it can block most of the high-energy stuff and we only see optical or infrared light. There s a whole menagerie of active galaxy types out there.
Quasars tend to have a lot of high-energy light (the first was discovered by its X-ray emission) and early on were also seen to be powerful sources of radio energy. But as we learned more we found that radio-loud quasars