Starship Asterisk*

https://www.eso.org/public/videos/eso2119b/ wrote:

Click to play embedded YouTube video.

This animation shows the orbits of the stars S29 and S55 as they move close to Sgr A* (centre), the supermassive black hole at the heart of the Milky Way. As we follow the stars along in their orbits, we see real images of the region obtained with the GRAVITY instrument on ESO’s Very Large Telescope Interferometer (VLTI) in March, May, June and July 2021. In addition to S29 and S55, the images also show two fainter stars, S62 and S300, the latter having only been discovered following these new VLTI observations.

https://www.syfy.com/syfy-wire/bad-astronomy-milky-way-black-hole-sgr-a-mass-measured-by-star-motions wrote:
<<They were able to determine the mass of the Sgr A* to be: 4.297 million solar masses (±0.25%) and the distance from the Earth to the center of the galaxy: 26,983 (±29) light years.>>

https://en.wikipedia.org/wiki/Sagittarius_A* wrote:

Inferred orbits of 6 stars around supermassive black hole candidate Sagittarius A* at the Milky Way's center

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<<Observations of several stars orbiting Sagittarius A*, particularly star S2, have been used to determine the mass and upper limits on the radius of the object. Based on mass and increasingly precise radius limits, astronomers have concluded that Sagittarius A* is the Milky Way's central supermassive black hole. Reinhard Genzel and Andrea Ghez were awarded the 2020 Nobel Prize in Physics for their discovery that Sgr A* is a supermassive compact object, for which a black hole is the only currently known explanation.

There are a number of stars in close orbit around Sagittarius A*, which are collectively known as "S stars" in various catalogues. These stars are observed primarily in K band (an atmospheric transmission window centered on 2.2 μm) infrared wavelengths, as interstellar dust drastically limits visibility in visible wavelengths. This is a rapidly changing field—in 2011, the orbits of the most prominent stars then known were plotted in the diagram at right, showing a comparison between their orbits and various orbits in the solar system. Since then, S62 and then S4714 have been found to approach even more closely than those stars.

The high velocities and close approaches to the supermassive black hole makes these stars useful to establish limits on the physical dimensions of Sagittarius A*, as well as to observe general-relativity associated effects like periapse shift of their orbits. An active watch is maintained for the possibility of stars approaching the event horizon close enough to be disrupted, but none of these stars are expected to suffer that fate. The observed distribution of the planes of the orbits of the S stars limits the spin of Sagittarius A* to less than 10% of its theoretical maximum value.

As of 2020, S4714 is the current record holder of closest approach to Sagittarius A*, at about 12.6 AU, almost as close as Saturn gets to the Sun, traveling at about 8% of the speed of light. These figures given are approximate, the formal uncertainties being 12.6±9.3 AU and 23,928±8,840 km/s. Its orbital period is 12 years, but an extreme eccentricity of 0.985 gives it the close approach and high velocity.>>

Chris Peterson wrote: ↑Sat Dec 05, 2020 3:24 pm

VictorBorun wrote: ↑Sat Dec 05, 2020 3:21 pm

Chris Peterson wrote: ↑Sat Dec 05, 2020 4:42 am
We know that there is a central black hole in the Milky Way because it is the only explanation for the orbits of the stars at the very center.

Do those orbits prove that the central BH is not a binary system with a period of 10 hours, to ruin 5 hours exposure in 2017?

Do those orbits prove that the central BHs are not several with a distance of 100 ly between them — one of them radio-bright and becoming a focus of the astronomic attention?

The orbits are consistent with a point source central BH.

https://en.wikipedia.org/wiki/Sagittarius_A* wrote:

Inferred orbits of 6 stars around supermassive black hole candidate Sagittarius A* at the Milky Way's center

---

<<Observations of several stars orbiting Sagittarius A*, particularly star S2, have been used to determine the mass and upper limits on the radius of the object. Based on mass and increasingly precise radius limits, astronomers have concluded that Sagittarius A* is the Milky Way's central supermassive black hole. Reinhard Genzel and Andrea Ghez were awarded the 2020 Nobel Prize in Physics for their discovery that Sgr A* is a supermassive compact object, for which a black hole is the only currently known explanation.

There are a number of stars in close orbit around Sagittarius A*, which are collectively known as "S stars" in various catalogues. These stars are observed primarily in K band (an atmospheric transmission window centered on 2.2 μm) infrared wavelengths, as interstellar dust drastically limits visibility in visible wavelengths. This is a rapidly changing field—in 2011, the orbits of the most prominent stars then known were plotted in the diagram at right, showing a comparison between their orbits and various orbits in the solar system. Since then, S62 and then S4714 have been found to approach even more closely than those stars.

The high velocities and close approaches to the supermassive black hole makes these stars useful to establish limits on the physical dimensions of Sagittarius A*, as well as to observe general-relativity associated effects like periapse shift of their orbits. An active watch is maintained for the possibility of stars approaching the event horizon close enough to be disrupted, but none of these stars are expected to suffer that fate. The observed distribution of the planes of the orbits of the S stars limits the spin of Sagittarius A* to less than 10% of its theoretical maximum value.

As of 2020, S4714 is the current record holder of closest approach to Sagittarius A*, at about 12.6 AU, almost as close as Saturn gets to the Sun, traveling at about 8% of the speed of light. These figures given are approximate, the formal uncertainties being 12.6±9.3 AU and 23,928±8,840 km/s. Its orbital period is 12 years, but an extreme eccentricity of 0.985 gives it the close approach and high velocity.>>

VictorBorun wrote: ↑Sat Dec 05, 2020 3:21 pm

Chris Peterson wrote: ↑Sat Dec 05, 2020 4:42 am We know that there is a central black hole in the Milky Way because it is the only explanation for the orbits of the stars at the very center.

Do those orbits prove that the central BH is not a binary system with a period of 10 hours, to ruin 5 hours exposure in 2017?
Do those orbits prove that the central BHs are not several with a distance of 100 ly between them — one of them radio-bright and becoming a focus of the astronomic attention?

Chris Peterson wrote: ↑Sat Dec 05, 2020 4:42 am We know that there is a central black hole in the Milky Way because it is the only explanation for the orbits of the stars at the very center.

VictorBorun wrote: ↑Sat Dec 05, 2020 4:15 am

sillyworm 2 wrote: ↑Fri Dec 04, 2020 12:35 pm There is actually speculation that a central black hole might not exist? How could that even be possible?

Well, are we really sure that there is a central BH in the Milky Way? The Event Horizon Telescope project tried to image it with few hours exposure and failed to get any crisp picture to publish (unlike M87*). What if there is really a binary BH system with an orbit's period of a few hours? A ternary system?
We know that statistically a large star or BH in a galaxy disk would drift toward the center after most encounters (and a smaller star would drift outward). But near the center the galactic gravitational pull is weak and the large stars or BHs there would be asymptomatically free, would not they?

sillyworm 2 wrote: ↑Fri Dec 04, 2020 12:35 pm There is actually speculation that a central black hole might not exist? How could that even be possible?

johnnydeep wrote: ↑Fri Dec 04, 2020 9:50 pm

Chris Peterson wrote: ↑Fri Dec 04, 2020 6:10 pm

johnnydeep wrote: ↑Fri Dec 04, 2020 5:03 pm

I agree that the negative image is fascinating, but I marvel that anyone can pick out the satellite galaxies. Seems to me that plenty of other candidate "smudges" could just as well be satellite galaxies. I wonder how they determine which are the real ones? Here's the negative:

Satellite galaxies will have similar redshifts to the large galaxy. Small smudges that are not satellite galaxies are much more distant, and will therefore be more redshifted.

So, are they able to get redshift measurements from all (or lots of) the smudges at once, or do they have to manually pick likely candidates and take separate measurements?

Chris Peterson wrote: ↑Fri Dec 04, 2020 6:10 pm

johnnydeep wrote: ↑Fri Dec 04, 2020 5:03 pm

sillyworm 2 wrote: ↑Fri Dec 04, 2020 12:28 pm Loving this apod..esp with the negative view showing the sattelites.What is that odd faint ghostly galaxy slightly past 12:00? Could it be an additional sattelite?

I agree that the negative image is fascinating, but I marvel that anyone can pick out the satellite galaxies. Seems to me that plenty of other candidate "smudges" could just as well be satellite galaxies. I wonder how they determine which are the real ones? Here's the negative:

Satellite galaxies will have similar redshifts to the large galaxy. Small smudges that are not satellite galaxies are much more distant, and will therefore be more redshifted.

johnnydeep wrote: ↑Fri Dec 04, 2020 5:03 pm

sillyworm 2 wrote: ↑Fri Dec 04, 2020 12:28 pm Loving this apod..esp with the negative view showing the sattelites.What is that odd faint ghostly galaxy slightly past 12:00? Could it be an additional sattelite?

I agree that the negative image is fascinating, but I marvel that anyone can pick out the satellite galaxies. Seems to me that plenty of other candidate "smudges" could just as well be satellite galaxies. I wonder how they determine which are the real ones? Here's the negative:

sillyworm 2 wrote: ↑Fri Dec 04, 2020 12:28 pm Loving this apod..esp with the negative view showing the sattelites.What is that odd faint ghostly galaxy slightly past 12:00? Could it be an additional sattelite?

APOD Robot wrote: ↑Fri Dec 04, 2020 5:05 am Curly Spiral Galaxy M63

Explanation: A bright spiral galaxy of the northern sky, Messier 63 is nearby, about 30 million light-years distant toward the loyal constellation Canes Venatici. Also cataloged as NGC 5055, the majestic island universe is nearly 100,000 light-years across, about the size of our own Milky Way. Its bright core and majestic spiral arms lend the galaxy its popular name, The Sunflower Galaxy, while this exceptionally deep exposure also follows faint, arcing star streams far into the galaxy's halo. Extending nearly 180,000 light-years from the galactic center the star streams are likely remnants of tidally disrupted satellites of M63. Other satellite galaxies of M63 can be spotted in this remarkable wide-field image, made with a small telescope, including five newly identified faint dwarf galaxies, which could contribute to M63's star streams in the next few billion years.

I guess I just wanted to see what all the fuss is all about when you read on the internet astro forums regarding optics that are made to be about as perfect as possible. Would it be worth the ultra-high price? Well to scratch this itch I decided that I would buy an Astrophysics of TEC APO. These two brands of American made refractors are widely regarded as the best that money can buy. After some searching I pulled the trigger on a used TEC 140!

The TEC 140 is a 140mm(5.5”) APO that is made 100% in the state of Colorado by a team of gents that came from the former Soviet Union. The scope has a focal length of 980mm and weighs in at a very manageable 19lb. So what’s the verdict on the best optics that money can buy?