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Astronomers Find Star Orbiting a Black Hole At 1 Percent the Speed of Light (sciencealert.com) 124

schwit1 writes: Astronomers have spotted a star whizzing around a vast black hole at about 2.5 times the distance between Earth and the Moon, and it takes only half an hour to complete one orbit. To put that into perspective, it takes roughly 28 days for our Moon to do a single lap around our relatively tiny planet at speeds of 3,683 km(2,288 miles) per hour. Using data from an array of deep space telescopes, a team of astronomers have measured the X-rays pouring from a binary star system called 47 Tuc X9, which sits in a cluster of stars about 14,800 light-years away. The pair of stars aren't new to astronomers -- they were identified as a binary system way back in 1989 -- but it's now finally becoming clear what's actually going on here. When a white dwarf pulls material from another star, the system is described as a cataclysmic variable star. But back in 2015, one of the objects was found to be a black hole, throwing that hypothesis into serious doubt. Data from Chandra has confirmed large amounts of oxygen in the pair's neighborhood, which is commonly associated with white dwarf stars. But instead of a white dwarf ripping apart another star, it now seems to be a black hole stripping the gases from a white dwarf. The real exciting news, however, is regular changes in the X-rays' intensity suggest this white dwarf takes just 28 minutes to complete an orbit, making it the current champion of cataclysmic dirty dancers. To put it in perspective, the distance between the two objects in X9 is about 1 million kilometers (about 600,000 miles), or about 2.5 times the distance from here to the Moon. Crunching the numbers, that's a journey of roughly 6.3 million kilometers (about 4 million miles) in half an hour, giving us a speed of 12,600,000 km/hr (8,000,000 miles/hr) - about 1 percent of the speed of light.
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Astronomers Find Star Orbiting a Black Hole At 1 Percent the Speed of Light

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  • by 140Mandak262Jamuna ( 970587 ) on Friday March 17, 2017 @04:01AM (#54056611) Journal
    Km and miles are useless in visualizing this. Please tell me how many schools buses lined up end-to-end will cover the distance between them.
  • by Anonymous Coward

    With the tidal forces this star has to be shaped like a big bent line whipping through space. I imagine pretty massive to keep a elongated core at critical mass as it whips around this star. It might be able to turn even a red giant into a super long white dwarf by stretching out the layers and surface area.

    • If it's a white dwarf (WD), it's going to have an internal strength (stiffness) somewhere well above that of steel, but more importantly, very strong forces pulling it's material back together.

      My non-calculated estimate on the WD's shape is that it would be a prolate ellipsoid of rotation, with the long axis pointing towards the primary. Not necessarily directly at the primary - there might be some displacement due to the residual rotational angular momentum of the WD.

  • I'm wondering about how quickly such a system loses energy. In general relativity, not even Keplerian orbits should be stable.
  • I wonder, how long it will take for the star to fall into the black hole? Or it will completely evaporate sooner? And how the orbit looks like?

    • by Anonymous Coward

      Probably more time than it takes the project to have its budget cut.

  • by Harold Halloway ( 1047486 ) on Friday March 17, 2017 @08:09AM (#54057267)

    Here in the UK, our press uses the following units of measurement:

    Distance: buses parked end-to-end.
    Weight: elephants.
    Area: Wales.

    Please amend the article appropriately.

    • by mjwx ( 966435 )

      Here in the UK, our press uses the following units of measurement:

      Distance: buses parked end-to-end.
      Weight: elephants.
      Area: Wales.

      Please amend the article appropriately.

      Are they an American or European bus.

    • Slashdot rule# 2 - if you can't complain about the topic, complain about the measurement units.
      • by clovis ( 4684 )

        Slashdot rule# 2 - if you can't complain about the topic, complain about the measurement units.

        Why on earth would you use a hyphen in that sentence?

    • Blue wales or humpback wales?
      And when would a British person ever see wales? Water is cold and wet so they don't go in it.
      Why would a British person want to see wales too.

  • Astronomers have spotted a star whizzing around a vast black hole

    Black holes are the antithesis of vast. They have no size whatsoever.

    • by Anonymous Coward

      Black holes are the antithesis of vast. They have no size whatsoever.

      I realise you're trying to be pedantic, but you're not trying hard enough. When we talk about Black holes, we mean the phenomena. As such, some black holes can be vast, since we consider the "hole" to be defined by its Schwarzschild radius. Now, if you're talking about the singularity at the centre of a black hole, that would be another matter.

    • by abies ( 607076 )

      From https://en.wikipedia.org/wiki/... [wikipedia.org]
      "Note that a black hole is a spherical region in space that surrounds the singularity at its center; it is not the singularity itself"

      So 'black hole' has the size, which is directly related to its mass. You can compute it here
      https://www.vttoth.com/CMS/phy... [vttoth.com]

    • by Bengie ( 1121981 )
      They're at least 1 cubic plank-length. Not to mention the notion of a true singularity is probably wrong. There's a lot of magic hand-waving to think of a blackhole as a true singularity. Some how the blackhole can grow, yet nothing can fall past the event horizon in any frame of reference, and all of the information is at the "center"? What? How does the information get to the center if by definition it can not?

      The more recent idea that a blackhole is just the highest density of information with the inf
  • The difference in force from gravity on the near side of the star compared to the far side must be enormous.

    Does anyone know how close this star is to its Roche limit, or equivalent for gaseous bodies?

    • this is why I like /., now I know what the Roche limit [wikipedia.org] is.
    • by edmor ( 4903597 )
      You're right. The tidal force must be huge. Especially since the orbiting star is losing mass to the black hole it cannot be in a perfectly circular orbit but must be somewhat eccentric. And those massive changes in gravitational forces it's subjected to are cycling over the space of just a few minutes! To add to the question about how close the star is to the Roche limit, does anybody know the mass of the black hole it's orbiting? How close is it to the black hole's event horizon? It would be very cool if
  • Everybody knows that only photons can reach the speed of light in vacuum.
    What happens with a solid object if we are starting to accelerate it?
    To what speed can it accelerate without losing its physical parameters (by ionization, atomic reactions etc)?

    • Mass does not lose its "physical parameters"-

      But the closer it comes to the speed of light the heavier it gets, it gains mass. That means, to accelerate it further, you need more power, but mostly you will again: just increase its mass and not its speed. Hence it can not reach the speed of light.

      However in labs we accelerate electrons or protons to something like 99.9% of c.

      • by WetCat ( 558132 )

        Mass doesn't lose its "physical parameters"e, true. But a physical object does! I have a spaceship. It is accelerating by some means. My question is: at what speed approximately it becomes a "set of protons and electrons" instead of its normal shape? To what speed it can accelerate without losing its shape?

        • My question is: at what speed approximately it becomes a "set of protons and electrons" instead of its normal shape? At none?
          To what speed it can accelerate without losing its shape? As close to c as you want, why do you think your ship would lose its shape?

  • I was thinking, "this is great! I can go hang out there for a few days and come back to Earth years from now".

    Unfortunately, 1% only gives a time dilation of about 1.01

        t' = t/sqrt(1 -v2/c2)

    Really, you have to get to well over 90% the speed of light if you want Trump's presidency to be over in a few hours.

  • by careysub ( 976506 ) on Friday March 17, 2017 @01:14PM (#54059723)

    That would be S0–2, a star orbiting Sagittarius A* - the gigantic black hole at the Milky Way's center.

    S0-2 has a longer orbit than 47 Tucanae X9, because it is highly elliptical, but at closest approach to Sagittarius A* is reaches 5000 km/sec. The speed of 47 Tucanae X9 is 3500 km/sec.

  • This has been out for twelve hours and even though TFS says "whizzing around a vast black hole", not ONE comment about "your Mom" or "Uranus"?

    Are we getting THAT old?
  • What kind of time dilation effects are we talking?

  • 1% the speed of light eh? and yet my g/f complains I go to fast ;)

Those who do things in a noble spirit of self-sacrifice are to be avoided at all costs. -- N. Alexander.

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