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Physics, Astronomy & Cosmology / Re: Orbiting or descending into the black hole at the centre of the Milky Way?

« on: 27/11/2022 20:49:35 »

Mainly the MW is in orbit around itself.

And the mass of the Milky way is dominated by the (so far) invisible Dark Matter halo.

it looks like the stars are swirling down into the black hole

Out in the fringes (where we live), the stars are well-separated, most of the stars are in a fairly thin disk, have fairly circular orbits, and and have roughly the same angular velocity. So they won't interact very strongly with each other.

However, in the central bulge, stars are closely spaced, they have wildly different orbital planes, and the ones we can see near the central black hole have rather elliptical orbits, so the stars will transfer angular momentum between each other.

Some of these gravitational interactions will "cancel" angular momentum (if the stars have different orbital axes).
I expect that this will result in the central bulge flattening out over time - but the average distance from the central black hole will then be less than it is now. When stars are moving in a disk, they will have fairly stable orbits.

...that is, until the central black hole merges with another black hole; the incoming black hole will add angular momentum into the system on an entirely different axis, and once again send the stars off in all directions.
https://en.wikipedia.org/wiki/Sagittarius_A*_cluster

it looks like the stars are swirling down into the black hole

You inferred this from looking at a still image, and imagining the galaxy as a drain emptying in a whirlpool. This is not what "Whirlpool Galaxy" means.
https://www.nasa.gov/feature/goddard/2017/messier-51-the-whirlpool-galaxy

The Gaia space probe has been able to measure the velocity of stars in the Large Magellanic Cloud, and it is showing the stretching associated with being spaghettified by its close approach to the Milky Way. But the orbits are still roughly elliptical, rather than converging on the central black hole (if it has one...)
https://www.esa.int/ESA_Multimedia/Images/2018/04/Rotation_of_the_Large_Magellanic_Cloud#.Y4PLHulNzqU.link

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Physics, Astronomy & Cosmology / Re: Orbiting or descending into the black hole at the centre of the Milky Way?

« on: 27/11/2022 17:55:10 »

The black hole has a mass of about 4.154±0.014 million solar masses.
The milky way has something like  100 thousand million stars
So, if the sun is a "typical" star only about 1 in 25000 of the mass of the milky way  is due to the BH in the middle.
If that BH disappeared it wouldn't make much difference to the motion of the sun.
Mainly the MW is in orbit around itself.

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Physics, Astronomy & Cosmology / Re: Orbiting or descending into the black hole at the centre of the Milky Way?

« on: 27/11/2022 16:52:02 »

To build on what Halc said about the spiral arms.  They are produced by compression waves moving through the galaxy. This induces a greater rate of new star formation within them.  So they tend to have a higher percentage of young stars.  The brighter the star, the faster it goes through its fuel, and the shorter its lifetime.  By the time a newly born really bright star leaves the spiral arm, it has passed its lifetime as a main sequence star and is a husk of its former self.  The stars that tend to live long enough to leave the spiral arm it was born in are the medium to dim stars.
In other words, the spiral arms look bright not because they are made up of a significantly higher concentration of stars or total material, but because they contain a higher ratio of young, bright stars.

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Physics, Astronomy & Cosmology / Re: Orbiting or descending into the black hole at the centre of the Milky Way?

« on: 27/11/2022 15:07:20 »

The portrayals of our galaxy do not look like Saturn's rings, but the stars look like they are going into the centre rather than  simply orbiting the centre with a circle or elliptical rotation.

You seem to be interpreting the portrayals as a stationary pattern along which the stars move. Both of these assumptions are wrong. The spiral pattern rotates, and at a rate considerably faster than once every 200 million years, so if the stars kept in their respective arms, they'd be traveling outward and would exit the galaxy after less than half a billion years. But no, the stars follow a generally circular path around the galaxy and move from one arm to the next as each overtakes our solar system in turn. The spaces between the arms are about as filled with stars of our magnitude as is the spaces within the arms, but it has far fewer short-lived bright stars that make the arms so visible.

All that said,

Looking at the Milky Way, it looks like the stars are not orbiting but swirling down into the black hole at the centre of the Milky Way.

There are some stars (a hundred or so?) that actually orbit the central black hole (Sgr-A), numbered S1, S2, ...
They're all quite large and I think we just cannot see the smaller ones. We're not one of those stars. The sum of our kinetic energy relative to Sgr-A plus the potential energy relative to Sgr-A is positive, and it must be negative for us to be in orbit about it. That's pretty much the definition of an orbital relationship, at least with only two objects. Only those S1... stars have negative total orbital energy relative to Sgr-A, which is actually a very small black hole for a galaxy our size, notorious for low rate of incoming new material.

It seems to me that our solar system is orbiting down closer and closer to the centre of the galaxy rather than remaining at the same distance.

It's actually getting further away slowly, for the same main reason Earth is moving away from the sun: The mass of the galaxy is decreasing as it consumes matter via fusion reactions. This raises our potential energy which correspondingly increases our orbital distance. That effect is greater than the other four processes (friction, random interaction with nearby masses, tides, gravitational waves) that also change that distance.

It takes millions of years for one solar orbit.

Between 200 and 250 million years in a not-particularly circular or even elliptical path.

Is this true that the stars are falling, swirling down into the increasingly strong gravity of the black hole in the centre?

The gravitational pull of our galaxy is decreasing, not increasing. Dropping a star into the black hole would probably increase our orbit a tiny bit just like dropping Mercury into our sun would likely result in Earth orbiting a tiny bit further away.

Could this mean the solar year is getting shorter?

Solar year is one trip of Earth around the sun. You mean the galactic year, and it is probably sufficiently variable from one orbit to the next that these cumulative changes would be overwhelmed by the noise.

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Plant Sciences, Zoology & Evolution / Re: Evolutionary DNA Leaps in Chromosome counts?

« on: 06/08/2022 01:42:49 »

Chromosomes can merge (reducing the count of chromosomes) or split (increasing the number of chromosomes).
- Recent research has found that use of CRISPR can chop up a chromosome, leaving a "spare" bit floating around in a cell nucleus
- Neither of these processes need be immediately fatal to a cell, since you still have the same number of genes
- The problem comes when the cell divides - does each "daughter" cell still have a full set of genes?
- And in the next generation of organism - do they still have a full set of genes?

The centromere is a structure in the center of each chromosome that plays a vital role in duplicating DNA into each daughter cell.
- A split-off portion of a chromosome may lack a centromere, inhibiting gene replication (or sometimes, a new centromere may appear)
- Two joined chromosomes may have two centromeres, which leads to chromosome breakage
- So most cases of chromosome splitting or joining are bad for the individual organism (often leading to cancer) and the descendents (who will suffer high rates of genetic disease and infertility with the parent species)
- But in rare cases, a descendent will receive two copies of the same mutation, allowing speciation
- Gene sequencing can identify cases where chromosomes have split or joined, since biologists can compare which genes occur on which chromosome.
See: https://en.wikipedia.org/wiki/Centromere

The leap from 46 or 44 Chromosomes to a working group of 48 chromosomes in the new species to be Gorillas

The human genome appears to be the result of the fusion of two chromosomes that remained separate in other primates (ie humans went from 48 to 46, while gorillas & chimpanzees remained at 48).
- So "progress" (new species) do not always come from splitting chromosomes (fission).
- New species can come from fusion, too.
https://www.mun.ca/biology/scarr/Human_Ape_chromosomes.htm

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Physics, Astronomy & Cosmology / Re: Formation of our solar system, the Nova, Nebula, dust and disc formation?

« on: 06/06/2022 16:16:53 »

Gold in our solar system, in the earth's crust formed in a nova or super nova, also everything heavier than iron, true?

Yes.

Was this a nova or super nova event? Was this about five billion years ago?

There were probably several nova and super nova that contributed heavy elements to the dust clouds that eventually became our solar system.

What and where is the remnant of this star and explosion?

White dwarfs, neutron stars and black holes.  They are long gone from our region of space.

Was there a resulting nebula? If so, what happened to it? Why wasn't there a resulting dwarf star or neutron star?

All these things are long gone.  4.5 billion years is a long time, we have orbited the milky way about 20 times since this happened.  In as little as 100,000 years the night sky will no longer have any recognizable constellations due to the motion of the stars.

Did our solar system form from a nebula or where did the mass come from, for the sun and planets?

It formed from a dust cloud or more correctly it formed from a 'molecular cloud'.

Do nebulas have a life span?

Yes.  There are many types of nebulas, but none of them are permanent features.  The quick answer on what happens to them is they either dissipate or coalesce.

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Physics, Astronomy & Cosmology / sIRe: The early Sun at the time just after Thea's impact?

« on: 06/06/2022 15:57:09 »

I assume after the impact there would not be a moon for quite a while.  There would be a debris field in orbit around the earth that would gradually coalesce into the moon.  Further I assume that there would be so much dust and debris in the atmosphere that you would not see the sun at all, the surface of the earth would be in darkness.

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Just Chat! / Re: The Hardy Question, about perception of something supernatural?

« on: 18/11/2020 08:45:53 »

I think Carl Jung is the founder of Psychology and Freud the founder of Psychiatry.

No, analytical psychology and psychoanalysis respectively, subsets of Psychology and Psychiatry.

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Geek Speak / Re: Windows 7 full version or original?

« on: 10/09/2020 19:09:13 »

Get the proper - trustworthy - impression from MS - use the create install media system:

https://www.microsoft.com/en-us/software-download/windows7

You can input your key; it will release the software if the key's valid.

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Just Chat! / Re: When have religious gatherings been illegal?

« on: 07/09/2020 23:15:18 »

you don't know anything about Jesus except via the writings of those " creedalists who heard the Gospel only in latin".

As I understand it, the Gospel writings attributed to Matthew, Mark, Luke and John were originally written in Greek. Greek copies exist, and are used for modern translations of the Bible.

These Greek texts were later translated into Latin, which became the "official" language of the Bible for over 1,000 years.

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Plant Sciences, Zoology & Evolution / Re: Insects and lizards, convergent evolution?

« on: 09/03/2020 14:33:48 »

My understanding is that some of this (similarities between lizards and insects) is convergent evolution, and some is due to shared primordial ancestry.

Lizards, being vertebrates, are evolutionarily descended from fish. Fish already had heads with eyes and mouths, internal skeletons, and appendages for locomotion. Fins are not so great on land, but provided a starting point for evolution of legs.

Insects, being arthropods, are evolutionarily descended from marine arthropods. (I am imagining shrimp-like critters).

Both split off from what would eventually become mollusks, and as such have some genetic and structural similarities (like bilateral symmetry, and digestive tracts).

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Physics, Astronomy & Cosmology / Re: The Moon from Earth 4 billion years ago?

« on: 15/09/2019 20:22:07 »

The Earth's sky without Ozone would not have been blue?

The ozone is not a major factor in the colour of the sky.
https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/why-is-the-sky-blue

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Physics, Astronomy & Cosmology / Re: The Moon from Earth 4 billion years ago?

« on: 15/09/2019 19:26:01 »

What would moon have looked like from Earth on a clear evening, 4 billion years ago? Was that not shortly before life formed on Earth?

Exact dates for both are not known, but it seems if life was barely there before the Theia event, that event would not have been kind to it.  Maybe..  Life in general is impossibly resilient, and if such an impact should happen today, life would most likely survive it.  Maybe life came from Theia itself.  Think about it.

It would have been extremely close! Immediately after it's formation from the Thea collision it must have resolved to a closest orbit, and moved away over time due to tides over millions of years?

The third of Kryptid's links gives distances, but oddly enough, not length of day or month.  I've heard the day would have been around 10 hours (and will be again if the sun can be prevented from swallowing us before then).  The calculations can be done with conservation of angular momentum laws.

At 4 billion years ago say 200 million years into it's life, the moon also had an atmosphere, coming from it's rocks and craters and internal sourced gases. What were those gases and what colours would they have been? And they would have been blowing in the solar wind, right? Under a dimmer colder sun?

Solar wind might have blown that atmosphere away almost as fast as it was emitted from the rocks.  Unclear if any appreciable pressure ever built up, but your subsequent link says yes, perhaps around 1% Earth's current pressure.

The Earth at this time along the equator, would not have had any land not swept over by the tide during the week?

Oceans took a long time to form after the Theia event.  Don't think tides ever swept clean over the continents.
I've heard of weather forecasts for back then: Hurricanes with mercury pressure down to about 15 cm, strong enough to polish the landscape down to smooth rock.

How many hours would a lunar orbit have taken back then?

Right after the moon formed, less than a day.  Several hundred million years later, maybe 4 days.

The point of centre of the two objects rotating would have been inside the Earth's diameter?

It still is, about 75% of the way to the surface.  Yes, it would have been deeper in back then.

Centrifugal forces would not have balanced out like with the Sun's gravity and the Earth's orbit?  Or is there a solar tide?

Don't know what you mean by centrifugal forces balancing out.  I think the moon's acceleration on Earth might have been as strong that that of the sun at some point.  It isn't close anymore.  The Earth always accelerates towards the sun even when the moon is full, pulling hardest in the opposite direction.  Yes, there have always been solar tides.  You're very aware of them if you live at sea level.

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Physics, Astronomy & Cosmology / Re: The Moon from Earth 4 billion years ago?

« on: 15/09/2019 17:45:16 »

This page goes into details about this very question: https://www.forbes.com/sites/quora/2018/07/11/what-did-the-moon-look-like-from-earth-4-billion-years-ago/#3cba74001151

These illustrations give visual comparisons of the Moon's appearance in the sky in the distant past: https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/

This calculator can tell you how long it took for the Moon to complete an orbit long ago: http://www.calctool.org/CALC/phys/astronomy/planet_orbit

At a distance of 15,000 kilometers, the Moon would have taken a bit over 5 hours to complete an orbit. At 20,000 kilometers, it's about 7.8 hours.

Given that most gases are colorless, Rayleigh scattering would have probably made the sky of the ancient Moon blue. It would have been darker than the Earth's sky, since it was a much thinner atmosphere (about 1% the pressure of Earth): http://www.astronomy.com/news/2017/10/moon-atmosphere

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Physics, Astronomy & Cosmology / Re: The Moon from Earth 4 billion years ago?

« on: 15/09/2019 17:42:35 »

I'm not sure how long you would have to wait after the (hypothetical) impact before the Earth's surface was cool enough to stand on.

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Physics, Astronomy & Cosmology / Re: What is the nature of dark matter around a black hole?

« on: 05/08/2019 14:00:01 »

It is thought that dark matter would be more concentrated in the center of the galaxy, nearer the supermassive black hole.

But because Dark Matter does not clump (like ordinary matter), it will not form an accretion disk, and will not radiate its energy via electromagnetism. This means that far more normal matter will fall into the black hole, even though Dark Matter is more common (by a factor of about 5).

Nobody is entirely sure what happens inside the event horizon of a black hole, but it seems likely that any Dark Matter that was aimed directly at the event horizon would find itself on a 1-way trip towards the central singularity. It will add to the overall mass/energy of the black hole.

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Physics, Astronomy & Cosmology / Re: What is the nature of dark matter around a black hole?

« on: 05/08/2019 12:03:47 »

What is the nature of dark matter around a black hole? Does it fall in? Is there dark matter in black holes? Is it repelled?

If it (a specific bit of it) is aimed quite perfectly, it will fall in.  More likely it picks up speed as it falls and exits the system similar to the way a comet leaves.   Maybe it orbits, or maybe it moves too fast to orbit.
It cannot be slowed or repelled since there is no way in interact with dark matter.  That's what makes it dark.

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Physics, Astronomy & Cosmology / Re: Proxima Centauri b and the red dwarf?

« on: 01/06/2019 16:25:50 »

If Proxima b is bigger than the earth, it may have a bigger magnetosphere, could this trap water?

We can compare Mercury and Venus, the latter is close to the Sun and has a very thick atmosphere. Smaller than the Earth, yet inside maybe more Iron?

The size of a planet has nothing to do with its magnetic field, which is generated by its spinning core.  One of the issues with orbiting so close to the star is that the planet is going to be tidally locked so that it rotation and orbit have the same period. Since Proxima b takes about 11 days to orbit, it would also take 11 days to rotate. The slower rotation doesn't bode well for generating a strong field. 
It is estimated that  Proxima loses mass to solar wind at a rate about 1/5 of that of our Sun, but Proxima b is only about 1/20 of the distance from its star than the Earth is from the Sun. This ends up with the Solar wind being more than 80 times stronger for Proxima b than it is for the Earth. 

While this does not completely rule out Proxima b from having a viable biosphere, it does but it at very long odds.

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Physics, Astronomy & Cosmology / Re: The Northern Stars and Exoplanets

« on: 31/05/2019 18:02:37 »

The present Northern star Polaris is actually a triple star system. the Primary star is a yellow giant some 2000 times brighter than our Sun, which also is a Cepheid variable, meaning its output varies over a set period, varying by about 8% over 4 days.  Its overall luminosity is also slowly increasing, having increased by ~2.5 times in the last 2000 yrs or so. 
The other two stars are also brighter than our sun, but only by about 3-4 times.
The main star is not a good candidate for planets due to its unstable nature, and the smaller of the other two is too close to the main star.   This leaves one star that could even possibly have some type of planet system.   However,  larger more massive stars spent less time in the main sequence. This star would only be expected to do so for about 1.5% as long as our sun.  Likely too short a time for any complex lifeforms to form.
Kochab, the "old" northern star is also more massive and brighter than our Sun.  It has also reached that part of its life cycle where it is beginning to expand into a giant.  Any planets it may have had are cooked by now.

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Chemistry / Re: Mercury, can you really safely dip your hand into?

« on: 29/01/2019 15:04:15 »

Yes. You can do it once or twice without any ill effect.

However, mercury is quite toxic. So how can this be?

Elemental mercury (ie the liquid metal) cannot easily pass through skin, so every time you touch it the dosage is incredibly small--each touch will deliver far less than a toxic dose. However, mercury is also very slow to leave the body, and can accumulate. This means that repeated exposure to small doses eventually adds up to a large dose.

Those who work with mercury on a regular basis without proper protection will be poisoned.

It is especially dangerous to heat mercury up, as it has a fairly high vapor pressure (for a metal--it boils at 360 °C). The vapors can condense in your lungs, and then will stay there until it has been absorbed (even though it is absorbed slowly, there isn't anywhere else for it to go, so you will get the whole dose).

Also, some compounds of mercury are MUCH more easily absorbed. Dimethylmercury is a notorious example. A single drop can pass through a rubber glove and through the skin within seconds, delivering a fatal dose (this has happened).