andrew s

The web site has gone. I found a link in a BAA post I made about it. What's your interest in them? Regards Andrew

Sorry 😞. My mistake. I discovered a couple of candidate Be stars during a spectroscopic search but the Web site with them on seems to have gone missing. Regards Andrew

Try here . Regards Andrew Looks like the same link @SteveBz gave.

Always good to seeing someone take the path less travelled. Regards Andrew

Simple answer is we don't know enough about dark matter to know what happens if and when it collides with itself or normal matter. As @robin_astro pointed out one idea is that it is it's own anti particle in which case we would expect it to give off its energy as radiation - presumably electromagnetic. There are lots of good ideas but no experimental results to sort them out. Regards Andrew

Another layer ? I still like it though. Regards Andrew

I rather like that. A bit less exposure on the moon, so it showed some detail, and it would have been even better. Regards Andrew

Give me general relativity over existential philosophy any day. 😉 Regards Andrew

It does not need to "lose" momentum to "clump" on galactic scales. Dark matter, via the gravitational interaction, just converts its initial momentum into orbital momentum just as ordinary matter would. It's only when normal matter gets close enough for friction to come into play e.g. star, planet formation and accretion disks that energy and momentum are lost via EM radiation. Regards Andrew

Now look what you made me do! thanks Andrew

Sorry @JeremyS but it was a Takahashi Sky 90. Just totally underwhelming. Regards Andrew

There are no laws in art only opinions. Diffraction spikes rule ok. 😊 Regards Andrew

The idea that dark matter is in a halo around a spiral galaxy is misleading. Its distribution is similar to the of normal matter see here . As an example for NGC 3198. The bottom figure shows the density of normal matter (b) and darkmatter (h). So they have an additive gravitational effect holding the galaxy together while flattening the rotation curve. Regards Andrew

Indeed, but I am always amazed by what we do know 😊 Regards Andrew

I know that. I was pointing out an alternative approach based on speed measurement. One way to avoid systematic error, which are very difficult to identify, is to use very different techniques. As you say they oscillate so they should have some mass. There are a number of unexplained anomalies within the standard model of particle physics, as there are within the LCDM and come to that any theory you care to mention. They are still currently the best we have. It's not for lack of effort by theoretical physicist but no one seems to have made any significant advances in a long time. Regards Andrew

An indirect way to approach the mass of a neutrino is to measure its speed. This gives a speed difference from that of light of 2x 10^-9 from the supernova 1987A. Whatever the mass it's very small. When trying to measure a value you not only have to worry about statistical variations but also systematic errors. The latter are very hard to eliminate. As an example this is the history of the speed of light measurements There looks to be a systematic difference between the early and late results. Regards Andrew

It's imaginary it's up to you what you imagine. It's not that complex. 😊 Regards Andrew

Of course you can. We have "on shell" real mass and "off shell" virtual mass. As far as I know both are normal with respect to gravity. Here is an introduction. Regards Andrew

@Gfamily if you Google black holes, dark matter, primordial you will find lots of papers both on accretion rates and if primordial black hole were dark matter. Regards Andrew

Well it depends on your definition of recent. Hubble's law was established in 1929. Quantum entanglement was proposed by Einstein, Podolsky and Rosen in 1935. While pop science likes to sensationalise faster than light metric expansion and spooky action at a distance these are well known to working scientists as part of their day to day work. What you may not realise is that our classical world emerges from entanglement with the environment at large. You and I have our classical form due to our interaction with for example the CMB photons, the molecules of the atmosphere and light from the Sun. Regards Andrew

Yes it has to directly "impact" the BH event horizon. As you point out it can't join the accretion disc. Not sure it's a unique insight though. Regards Andrew

It accumulates at galactic scales not stellar or planetary. On galactic scales it doesn't need to lose angular momentum and energy as it would to form stars or planets. Trying to understand dark matter and dark energy is an ongoing research effort with considerable effort going in. Regards Andrew

Is dueling still legal in France? @saac will you be my second? Regards Andrew

I love them. They are made by real telescopes not toys. 😊 Regards Andrew

Well done @ollypenrice what it needs is some diffraction spikes on the bright stars to add impact and framing 🤣 Regards Andrew