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99.9% of all mass at center of Milky Way is found in central black hole

New measurements of the orbits of several stars circling the Milky Way’s central supermassive black hole, Sagittarius A* (pronounced A-star), have confirmed that 99.9% of all mass at the galaxy’s center is concentrated in that black hole.

Astronomers have measured more precisely than ever before the position and velocity of four stars in the immediate vicinity of the supermassive black hole that lurks at the center of the Milky Way, known as Sagittarius A* (Sgr A*) [1]. These stars — called S2, S29, S38, and S55 — were found to be moving in a way that shows that the mass in the center of the Milky Way is almost entirely due to the Sgr A* black hole, leaving very little room for anything else.

The measurements, which further refine the mass of Sagittarius A* as 4.3 million times the mass of the Sun, show that very little of this mass is found in the surrounding space as gas or dark matter. It is all in the black hole, which might also help explain why the Milky Way’s central black hole is so quiescent. It has very little gas or other stars to feed it and thus produce emissions.

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.


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  • Phill O

    Whatever any one can say is: Heavy man, really heavy.

  • MadRocketSci

    4.3 million solar masses is big, but there is something like 100 billion stars in the galaxy. I’ll have to read the paper to see how they are defining this “core region” devoid of other matter. The central bulge of the galaxy (~2-3000 LY thick) should be far more massive than the black hole.

  • MadRocketSci: I should have noted that compared to most central supermassive black holes, ours is somewhat small. It isn’t unusual for most to be several BILLION times the mass of the Sun, not million.

  • Doubting Thomas

    Isn’t this the same as the central part of the plot of Larry Nivens Neutron Star?

    Maybe we are just a simulation.

  • Robert noted: “I should have noted that compared to most central supermassive black holes, ours is somewhat small.”

    Do galaxies have Black Hole Envy?

  • Max

    Further reading. ( I particularly like other theories, especially the ones that don’t involve dark matter)
    The previous estimate was 4.1 million solar masses. (± 0.034)
    “Stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotational speed appears to contradict the laws of Keplerian dynamics”
    This would indicate that the effect of a supermassive black hole is limited in its reach (according to the inverse square law) of only a few light years before it’s gravity influence no longer can be felt. There is another force at work that cannot be explained by dark matter. (that seems to create more problems than it solves)

    Although my beliefs evolve as I learn more, I think it is a “collective attraction” of individual stars in close proximity that has the overall greater effect on the whole Galaxy. That’s why the outer disc and the inner bulge stars move at a similar speed maintaining a relative balance. (It would be expected that faster moving stars would be near large gravitational attractions like black holes… A dead giveaway)
    On the other hand, diffuse galaxies (which they’re finding more all the time) have much less mass and move accordingly, very slowly.

    It reminds of watching the diffusion of food coloring when making food for hummingbirds. It is erratic following random movements. (unless heat is applied, then it becomes predictable) But galaxies follow a different order similar to applying electricity to the water (12 to 24v DC) while placing a magnet underneath. The entire contents begins to slowly spin in an organized manner. Just as low pressure storms in our atmosphere spins in earths magnetic field.
    In appearance, I always thought galaxies had more in common with a hurricane than the Newtonian planetary model.

  • Star Bird

    Just when can we make the jump into Hyper Space?

  • Steve Richter

    Since galaxies are moving independently of each other, there are times when galaxies pass thru each other, correct? At which time the black holes of the two intersecting galaxies get to feed on a bunch of matter in their path. Have the central black holes of two galaxies ever been observed colliding?

  • wayne

    Galaxy Collisions: Simulation vs Observations
    Hubble Space Telescope (2014)

  • Jay

    Yes, it has been observed galaxies passing through each other. A lot of the loose hydrogen of those galaxies get together through gravity and form new stars. It is the hypothesis that our own Sun, which is considered young, was a creation of a colliding dwarf galaxy into the Milky Way.
    To answer your other question, yes, due to gravity the black holes rotate towards each other and it looks like a dance. These dancing black holes eventually collide and become one big black hole. It has been observed that this collision has emitted light.
    There are many simulations online about the collision of the Milky Way and Andromeda Galaxies. I might also recommend the PBS series Nova, they have been recently airing a multiple episode series about the universe and one of those episodes which focuses on the findings of the Gaia satellite which address your specific questions.

  • Steve Richter

    in the wikipedia page on gravitational waves it says the first waves detected in 2015 were the result of “… two black holes with masses of 29 and 36 solar masses merging about 1.3 billion light-years away…” How massive would the resulting gravitational wave be when galaxy center size black holes merge?

    Jay, thanks for the Nova tip. An aside, I search netflix DVD site. They have Nova episodes. But looks like their collection is only prior to 2011. So much for their presumed mission of making their educational material available to the public on mainstream web sites?

  • Jay

    Hi Steve,
    The episodes are free on the PBS site:

    I encourage you to watch all the episodes, but if you want to know about your questions about black holes and galaxies, watch the “Milky Way” and “Black Holes” episodes.

  • wayne

    Steve / Jay–
    Good deal.

    I consume a lot of space & physics video, just some quick resources to check out, for newer material Most easily found by searching youtube for their respective channels. For archival / historical material, search directly at Archive dot org. (which has a huge NASA film collection from the 1960’s)

    Perimeter Institute public lectures
    Gresham College Lectures
    Silicon Valley Astronomy Lectures
    PSW (Philosophical Society of Washington) Science Lectures.
    Space Science Telescope Institute Lectures
    Sean Carroll — Biggest Ideas In The Universe series
    Brian Keating – Into The Impossible video-cast series
    Leonard Susskind Lectures at Stanford
    Lex Fridman video-cast

  • Max

    I will have to spend some time looking up and refreshing on the latest science concerning the black hole theories.

    If stuff doesn’t make sense to me… I drag my feet believing in it.

    It’s been a while, I remember a discussion that under black hole theory, (which there are many different views depending on what aspects of the physics you use) they cannot Collide… When they get close enough together, a wormhole forms between two massive objects and the larger one sucks the other one dry like a drinking straw. The gravitational wave that is measured in a/ 10th of a second is actually the collapsing of the wormhole like a rubber band. When the subspace tunnel can no longer be maintained, the link is severed allowing the now much smaller object with exotic black hole matter to no longer have an event Horizon due to it’s reduction in mass, but able to broadcast brightly like a Quasar or magnetar…
    I believe the discussion was how quasars were found so far from their host galaxy, how were they expelled? Or did they eat all the stars in their host galaxy? And they’re finding another galaxy to consume?

    Most people focus on the gravity of a black hole… when time go longer exists it creates the same affect. (The laws of space-time cannot be separated) is it gravity that makes a black hole black? Or is it when “time” comes to a stop, photons leaving a star at only a few photons a second (from our perspective) is very difficult to detect? Especially when a photon at 400 nm wavelength passes through the resistance of the time/gravity field, is it recognizable as light… Or has it Red shifted into the microwave or sound wave length? (adjust your scanners for Omicron radiation, Spock)
    How does gravity escape that event horizon? (I believe gravity is a force like magnetism that occurs instantaneously, there is no delay in the Newtonian physics, unlike Einstein’s relativity time delay in satellites synchronization)

    I guess I’m just very skeptical, I was lied to about religion when I was a child (and Santa), lied to about the sun being a nuclear furnace (almost no radiation compared to the output) and lied to daily about CO2 causing a greenhouse effect (which violates the second law of thermodynamics).
    No mention in any of the climate models of the Chinook winds which holds the Guinness book of world records for temperature change (The ideal gas laws?) or the new attempt to scare people that sea levels will rise a meter because of a glacier breaking off of Antarctica… A failure to recognize the glacier is already displacing water.
    Or the report this morning the death rate for children has gone up 60% since September when the vaccines for children was rolled out in Britain… Just a coincidence.

  • Max

    As for Larry Niven, ring world, and the collection of every species the puppeteers could find to populate ring world… An attempt to relocate the survivors of our galaxy as the energy in a supernova chain reaction from the center of our galaxy move outward at the speed of light but taking thousands of years to reach us way out in the Orion spiral arm. We won’t even know it happened until it’s too late…
    “Sci-fi with a twist that expands the imagination”

  • wayne

    Miracle on 34th Street
    “Mr. Kringle is Santa Claus!”

  • Andi

    ” … magnetism that occurs instantaneously”

    To me, the propagation of EM waves at the speed of light would argue against instantaneous propagation of magnetism.

  • Max said: “I was lied to about religion when I was a child (and Santa)”

    What! I got Christmas presents from Santa every year, right there on the gift tag, (until my Mom passed). Sometimes, people appreciate willful suspension of disbelief (cf: entertainment). Santa is real Just ask NORAD.

  • Andi

    From that site: “ Rudolph’s nose gives off an infrared signature similar to a missile launch. The satellites detect Rudolph’s bright red nose with no problem”

    Love it!

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