Wikipedia:Reference desk/Archives/Science/2021 March 11

= March 11 =

Cure to aging question about women
If we will discover a successful cure to aging and manage to make an old post-menopausal woman young again, will this cure also result in this woman once again becoming fertile or would she actually need the implantation of new ovaries for that? Futurist110 (talk) 05:48, 11 March 2021 (UTC)
 * This is quite a hypothetical situation. If a woman was made young again you should expect everything in her to work the same way as a young woman, so yes she would likely be fertile. However if it was just a successful anti wrinkle treatment or a refresh of telomeres, or a cure for arthritis, or a clean up of cellular senescence then the answer would be no. Given your user name, you should be answering this! Graeme Bartlett (talk) 06:15, 11 March 2021 (UTC)
 * While the science is not as yet settled, there are suggestions that renewed fertility would likely not result from general rejuvenation.
 * Fertility depends on an ovarian follicle in one or other of the ovaries producing a mature ovum. Although female humans are born with millions of primordial follicles with the potential to mature, the number of these declines steeply with age, with only 10% remaining at around age 30. It appears that by around 55 there are few to none left, so subsequent rejuvenation by some as-yet-undiscovered means might restore the levels or hormones (whose decline cause the primary symptoms of the menopause) required to cause ovum maturation, but there would be no ovarian follicles left for them to work on.
 * Some additional means would have to be found either to cause the generation of new follicles, which has reportedly been observed in mice but not (yet) in humans, or to generate them in vitro from stem cells and implant them into the ovaries. If that were the procedure adopted, it would probably be more efficient to take the further step of generating mature ova in vitro and fertilise them ditto before implanting them into the womb as is already routinely done. {The poster formerly known as 87.81.230.195} 2.125.75.168 (talk) 10:21, 11 March 2021 (UTC)

Could there be primordial small black holes inside extremely big stars?
For example if a star had a mass 25 times the mass of the sun, could it be containing a black hole with a mass comparable to the Earth or Moon? Could it be a common occurrence, or even most common way for such a large star to form? What if more than one small black hole were inside, i suppose they would probably orbit. So would they necessarily collide early in the relatively short lifetimes of such big stars? Are there theoretical reasons or astronomical observations that preclude small black holes in big stars? Thanks. Rich (talk) 17:32, 11 March 2021 (UTC)
 * According to primordial black hole, such small black holes no longer exist; only primordial black holes greater in mass than about 100 billion kilograms should still exist; anything smaller would have evaporated by now due to Hawking radiation. There is some speculation that supermassive black holes, which are many times larger than even the biggest black holes known to form from stellar collapse and accretion, could have been formed by the largest of the primordial black holes, but I know of absolutely no hypothesized mechanism like you are describing to form ordinary stars.  It is not necessary to invoke primordial black holes to explain star formation, the mechanism is well understood and involves only the internal gravity of the nebula itself.  -- Jayron 32 17:42, 11 March 2021 (UTC)
 * From the article, primordial black holes with mass > 1011 kg will not have evaporated yet. The OP asks about a black hole mass similar to the Moon (7x1022 kg) or Earth (6x1024 kg), which are both well above this lower limit. If such black holes existed in the early universe, they could still be around. --Amble (talk) 18:54, 11 March 2021 (UTC)
 * hmm thanks, lets change my question to include black holes of mass 10^11 kg up to a mass significantly less than a solar mass.Rich (talk) 19:29, 11 March 2021 (UTC)
 * Sorry yes, I misinterpreted the scales. Forget my answer then.  It was of no help.  Well, except for the last sentence, which I still stand by.  -- Jayron 32 19:38, 11 March 2021 (UTC)
 * I believe the right way to back-of-the-envelope your first question is to treat it as Bondi accretion and find the time constant (mass divided by accretion rate) for growth of the black hole mass. If this is long compared to the lifetime of the star, we can say that the black hole could peacefully "hang out" inside without disrupting things too much. If the time constant is shorter, then something else will happen. The "something else" will be complicated (no longer just Bondi accretion) and can include possibilities like Quasi-stars or other exotic stars, but I expect will end in a core collapse supernova. --Amble (talk) 21:16, 11 March 2021 (UTC)
 * Let's take the star to be a main sequence star with a central density ~150 g/cm3 (solar core) and a sound speed 300 km/s (]). Then the Bondi calculation for a black hole with the mass of the Moon (7x1022 kg) gives a time constant of 6 years. That's too fast; the black hole grows too quickly and will disrupt the star. If we set the black hole mass to the minimum value (1011 kg), we get 4x1012 years. That's probably OK; that black hole could last for a long time inside a main sequence star. The cutoff where the time constant is equal to the age of the universe is 3x1013 kg. This paper on quasi-stars also considers a Bondi accretion model but treats an intermediate case where accretion onto the black hole powers the exotic star during its lifetime. I haven't found a paper that explicitly treats primordial-mass black holes captured by normal stars. There are papers about transient encounters, but there doesn't seem to be a good mechanism for the star to capture the black hole. --Amble (talk) 21:55, 11 March 2021 (UTC)
 * Okay but the very large stars(say 25 solar masses) last 100 million years or less.Rich (talk) 22:34, 11 March 2021 (UTC)
 * I’m mainly wondering about the case where the small black hole was in the star from the beginning, in a starforming nebula. Because how does a gas nebula “decide’ what size stars to form into?Rich (talk) 22:39, 11 March 2021 (UTC)
 * (So how it would get captured wouldn’t be a question if it were a “nucleus”, like a bit of dust a raindrop forms around.)Rich (talk) 22:43, 11 March 2021 (UTC)
 * Also if it was innside a star and it was small enough to evaporate while the star was minding its own business being a star, would it be a noticeable disruption when it evaporated, that we could observe?Rich (talk) 22:49, 11 March 2021 (UTC)
 * An evaporating black hole emits 2x1022 J in its final second . The solar luminosity is 4x1026 W. That means the final second of black hole evaporation is equivalent to 50 microseconds of solar luminosity. There would be nothing to see if that happened inside a star. There is literature on detectability of Hawking radiation, if you're interested. --Amble (talk) 18:59, 12 March 2021 (UTC)
 * Good news: I found just the right paper . Enjoy! --Amble (talk) 00:36, 12 March 2021 (UTC)
 * There are papers considering primordial black holes seeding structure in the early universe, which leads to star formation . However, it's not clear to me that the black holes would or should end up inside the resulting stars. It's a "cooling problem" that's actually not too different from the "capture problem" we talked about earlier. This is all about the earliest stars in the universe, which should have a very short lifetime and different characteristics from the stars we see today. In that case, if the black hole grows inside the star and disrupts it after a few million years, that's not necessarily a problem for the model (like the quasi-stars again). --Amble (talk) 01:16, 12 March 2021 (UTC)
 * Thank you, good answers.Rich (talk) 05:15, 12 March 2021 (UTC)

How can males cry if they have more testosterone count than females?
How can males cry if they have more testosterone count than females? Rizosome (talk) 18:44, 11 March 2021 (UTC)
 * Pardon my tone, but where on earth did you get the notion that crying is connected to testosterone levels? I've certainly never seen that anywhere?  Testosterone is primarily involved in the development of secondary sex characteristics, and you can read the article in question to learn what those are, but you'll see that "not crying" is not listed there anywhere.  Males may be acculturated (meaning "trained by their society") to not cry, but there is absolutely nothing biological about that; it's purely a cultural norm.  -- Jayron 32 19:07, 11 March 2021 (UTC)


 * I've known men who get emotional, and women who don't. It's a function of both nature and nurture. I've also always said that while men are trained to be strong, a man who can't cry at the loss of a loved one is not much of a man. ←Baseball Bugs What's up, Doc? carrots→ 22:14, 11 March 2021 (UTC)


 * As a child I was told a zillion times, "Big boys don't cry", and I'm sure that went in very deep and still affects me to this day. I always wondered why boys have tear ducts. --   Jack of Oz   [pleasantries]  23:56, 11 March 2021 (UTC)


 * I always heard it was big girls who didn't cry. DuncanHill (talk) 00:07, 12 March 2021 (UTC)
 * Boys neither. -- Jayron 32 12:13, 12 March 2021 (UTC)
 * That's just an alibi.--Khajidha (talk) 13:23, 12 March 2021 (UTC)
 * Tear ducts are like nipples. —Tamfang (talk) 01:58, 14 March 2021 (UTC)
 * They produce milk??? ←Baseball Bugs What's up, Doc? carrots→ 02:42, 14 March 2021 (UTC)

Difference between iron and steel
Is there a fundamental difference between "iron" and "steel", or is it just an arbitrary naming convention? I know that they are distinguished by carbon content, but "iron" can describe materials that have less carbon that steel does (elemental iron, wrought iron), and also materials with higher carbon content (pig iron, cast iron). Is there some fundamental material property that all "irons" share but "steels" don't, and vice versa? Or is it just a case of certain iron alloys have traditionally been called "steel", and all others "iron"? Iapetus (talk) 18:53, 11 March 2021 (UTC)
 * Do you mean "What is the difference, from a chemistry/metallurgy/materials science perspective between iron and steel?" or "What's with all of these people using words imprecisely, and why is it messing with my understanding of the difference between iron and steel?" Those are two different questions, but I will try to answer them both.  For the first question, iron is a chemical element, which is to say it is a substance composed of only one kind of atom, those being iron atoms.  Steel is an alloy, which is a type of solid solution: it consists of an element with another element dispersed in it; steel is iron with carbon dispersed in it.  The answer to the second question is "language is odd and imprecise and that's just the way it is".  Strictly speaking, pig iron and cast iron and wrought iron are steels, despite the name.  For reasons which would make your head spin, "steel" as a name is usually reserved for intermediate iron content alloys; both wrought iron (which has less carbon) and cast iron (which has more carbon) are not strictly considered steel; they are each too brittle to have the characteristics desired of useful steel.  -- Jayron 32 19:24, 11 March 2021 (UTC)
 * This is great, i’ve also wondered about this a long time! thanks Rich (talk) 19:31, 11 March 2021 (UTC)
 * I meant "Is there a scientifically justifiable reason for calling certain iron alloys 'steel', but others 'iron'?" I know that the word "iron" refers to an element (Fe) and also to certain low-carbon and high-carbon alloys, with steel being used for other alloys.  (I included all that info in my original question).  Iapetus (talk) 10:36, 15 March 2021 (UTC)
 * You could also say that steel is iron in which the impurities are considered a feature, not a bug. PiusImpavidus (talk) 09:01, 12 March 2021 (UTC)
 * Cast iron, as noted previously, actually has more carbon than steel. The nomenclature is confusing because it's the result of centuries of linguistic evolution. Modern chemistry and its understanding of elements and alloys is younger. Basically all iron in use outside of chemistry and physics is really an iron alloy, since iron reacts so readily with many chemicals. Teleologically, "steels" are iron alloys where the alloy composition is controlled to produce desired characteristics. Wrought and cast iron take less effort to produce, and are used in low-cost applications where the precise composition is not as important. --47.152.93.24 (talk) 20:59, 12 March 2021 (UTC)