Wikipedia:Reference desk/Archives/Science/2018 November 18

= November 18 =

Why do cats lick themselves when you scratch them near the base of the tail?
I've had at least two cats who do this. They lick their chests or their front paws. Is it a reflex? Is it an indication that they like it, that they don't like it, or neither one? --Trovatore (talk) 00:33, 18 November 2018 (UTC)
 * I've only seen females do that, though sometimes they just lick the air and chirp while looking in random directions. If they they tolerate the person doing so at all, they usually start purring and don't run off after.  That spot would be getting... friction during mating.
 * My mom's current male and my brother's male both like being patted there but not scratched, and only by their favorite individuals after a period of learning to trust that patting is all that's going to happen. In the case of my mom's cat, Gravy is either to be found tucking his head into my hand (to hell with whatever I'm doing or holding) or sitting next to my bedroom door singing "I Can't Stop Loving You".  My brother's cat is a complete misanthrope but deigns that my brother and his girlfriend should be exterminated last. Ian.thomson (talk) 00:58, 18 November 2018 (UTC)
 * My current Mama Cat (spayed female) licks her chest and seems to be OK with it, but it's hard to be sure. My late lamented Sox (neutered male), maybe the sweetest cat who ever lived, would sometimes lick his paws violently from a mere touch in that spot.  I got the sense that it distressed him so I tried to avoid it, although it seemed to come and go &mdash; I'm thinking maybe there was some intermittent skin condition or nerve problem. --Trovatore (talk) 01:08, 18 November 2018 (UTC)
 * This site says that cats generally do not appreciate being touched there. A study in Applied Animal Behaviour Science found likewise.  Most male cats I've encountered who were otherwise enjoying my presence would get angry if I tried to go there.  Females would either be confused at first or way too receptive to only males petting them there.  This is why I strongly suspect that that area has nerves that would be stimulated by having the receptive role in mating (which for most male cats would be disturbing for anyone they don't submit to). Ian.thomson (talk) 01:32, 18 November 2018 (UTC)

White dwarf -versus- Wolf-Rayet: who wins?
In one corner, we have R136a1, a Wolf-Rayet star, 50000K surface temperature, 315 solar masses. In the other, on a slow collision course, we postulate a puny white dwarf like one of the stars in SDSS J0106-1000, 0.17 solar masses, made of a condensed plasma 5000 times denser than anything we know on Earth.

Question: who wins this fight? Does R136a1 bring the heat of its core to bear, or of gas it dumps onto the oncoming challenger, to the point where the white dwarf unbinds and becomes a cloud of carbon and oxygen atoms again? Or does the aging supergiant take to condensed matter like a new religion, and become reorganized onto the white dwarf, while presumably ejecting a larger amount of material because the infalling material produces enough heat to blast it away? Or, for that matter, does some aspect of the interaction simply bat the white dwarf away like a grandmother beating off a rabid squirrel with her laptop? Wnt (talk) 00:33, 18 November 2018 (UTC)
 * The low mass helium white dwarf will quickly sink to the center of the WR star and will be quietly sitting there (surrounded by hot helium core material) and slowly evaporating. Otherwise there will be no changes in the appearance of the WR star. I can not say how much time it will take for the WD to completely evaporate. Ruslik_ Zero 20:21, 18 November 2018 (UTC)
 * I don't feel convinced. According to this the CNO cycle starts at 1.5 x 107 K, which seems comparable to the 1 x 107K figure our article on white dwarf gives.  True, this one is presumably well past that threshold, but on the other hand, well, the Sun has a density of 1 g/cc like water, and R136a1 has 315 solar masses packed into a radius about 30 times larger, which is to say, it has about an aerogel-like density (maybe it beats styrofoam at the middle, but I doubt it).  So if the innards of that star are a few times hotter than the white dwarf but now the gravity is increased from being proportional to styrofoam to tons-per-teaspoon, I am thinking the white dwarf is going to account for itself quite well ... unless, that is, there is a way to evaporate or destroy it first? Wnt (talk) 23:35, 18 November 2018 (UTC)
 * The temperature in the core of R136a1 is much higher than 15,000,000 K and CNO cycle is already taking place there. Although due to the age of R136a1 there is probably little hydrogen left. So, a low mass helium WD with diameter of about 2 Earth's diameters and density much high than that in the core might induce some local increase of hydrogen burning rate. This increase will probably be around a few tens Solar luminosities, which is negligible as compared to the total luminosity of R136a1 - more than 8,000,000 Solar luminosities. Ruslik_ Zero 13:43, 20 November 2018 (UTC)
 * There are no collision courses! The universe is full with Binary stars and systems containing multiple suns that circle each other in stable or even chaotic pattern for billions of years without colliding. Its a common misconception based on our bad habit to display stellar objects and their distance between each other totally out of proportion, to get a visual picture with all objects visible. But in reality, with the proper proportions most system objects become invisible, like normal humans cant see any other planet of our system unless gifted with very good sight or an telescope and the knowledge when to look where exactly at night under very good weather conditions. --Kharon (talk) 00:44, 19 November 2018 (UTC)


 * Collisions are not impossible, and the question asks us what the result would be if one happened, not how likely it is. --76.69.46.228 (talk) 06:59, 19 November 2018 (UTC)


 * I tend to think that the gravitational field of the white dwarf would start to force accretion of the expelled material from the WR star at quite an early stage. This could even spark the white dwarf into a nova state, and the whole system could possibly enter supernova. https://www.sciencedaily.com/releases/2009/09/090903163852.htm for a reference for this. --TammyMoet (talk) 13:00, 19 November 2018 (UTC)


 * By the way - you can't get a slow collision between two stars. Best you can do is have them circle around each other and gradually lose energy. Dmcq (talk) 22:17, 19 November 2018 (UTC)
 * As the previous reply indicates, this often then leads to a nova or type Ia supernova as the white dwarf siphons away matter from its companion. --47.146.63.87 (talk) 06:42, 23 November 2018 (UTC)