Stars Orbiting Close to Black Holes Flattened like Hot Pancakes

Playing with black holes is a risky business, especially for a star that is unlucky enough to be orbiting one. Assuming an unfortunate star hasn’t already had all of its hydrogen fuel and other component elements stripped from its surface, the powerful tidal forces will have some fun with the doomed stellar body. First the star will be stretched out of shape and then it will be flattened like a pancake. This action will compress the star generating violent internal nuclear explosions, and shockwaves will ripple throughout the tormented stellar plasma. This gives rise to a new type of X-ray burst, revealing the sheer power a black hole’s tidal radius has on the smaller binary sibling. Sounds painful…

It is intriguing to try to understand the dynamics near a supermassive black hole, especially when a star strays too close. Recent observations of a distant galaxy suggests the material pulled from a star near the center of a galactic nucleus caused a powerful X-ray flare which echoed from the surrounding molecular torus. The infalling stellar gas was sucked into the black hole’s accretion disk, generating a huge quantity of energy as a flare. Whether or not the star stayed intact for the duration of its death-spiral into the supermassive black hole it is unknown, but scientists have been working on a new model of a star orbiting a black hole weighing in at a few million solar masses (assuming the star can hold it together for that long).

The pancake effect of a star falling into the tidal radius of a black hole (J.-P. Luminet)

Matthieu Brassart and Jean-Pierre Luminet of the Observatoire de Paris-Meudon, France, are studying the effects of the tidal radius on a star orbiting close to a supermassive black hole. The tidal radius of a supermassive black hole is the distance at which gravity will have a far greater pull on the leading edge of the star than the following edge. This massive gravitational gradient causes the star to be stretched beyond recognition. What happens next is a little strange. In a matter of hours, the star will swing around the black hole, through the tidal radius, and out the other end. But according to the French scientists, the star that comes out isn’t the same as the star that went in. The star deformation is described in the accompanying diagram and detailed below:

  • (a)-(d): Tidal forces are weak and the star remains practically spherical.
  • (e)-(g): Star falls into the tidal radius. This is the point at which it is destined to be destroyed. It undergoes changes in its shape, first “cigar shaped”, then it gets squeezed as the tidal forces flatten the star in its orbital plane to the shape of a pancake. Detailed hydrodynamical simulations of shock wave dynamics have been carried out during this “crushing phase”.
  • (h): After swinging around the point of closest approach in its orbit (perihelion), the star rebounds, leaving the tidal radius and begins to expand. Leaving the black hole far behind, the star breaks up into clouds of gas.

As the star is dragged around the black hole in the “crushing phase” it is believed that the pressures will be so great on the deformed star that intense nuclear reactions will occur throughout, heating it up in the process. This research also suggests powerful shock waves will travel through the hot plasma. The shock waves would be powerful enough to produce a short (<0.1 second) blast of heat (>109 Kelvin) propagating from the star’s core to its deformed surface, possibly emitting a powerful X-ray flare or gamma-ray burst. Due to this intense heating, it seems possible that most of the stellar material will escape the black holes gravitational pull, but the star will never be the same again. It will be transformed into vast clouds of turbulent gas.

This situation wouldn’t be too hard to imagine when considering the dense stellar volume in galactic nuclei. In fact, Brassart and Luminet have estimated that there may be 0.00001 event per galaxy, and although this may seem low, future observatories such as the Large Synoptic Survey Telescope (LSST) may detect these explosions, possibly several per year as the Universe is transparent to hard X-ray and gamma-ray emissions.

Source: Science Daily

11 Replies to “Stars Orbiting Close to Black Holes Flattened like Hot Pancakes”

  1. Wouldn’t studying “Hot jupiters” also be a possible theory as to what it would be like with a star orbiting a black hole. I mean, the atmosphere of the gas giant is going to be ripped away and one could assume that the planets shape would also be flattened due to its fast rotation and forces against it

  2. Hi Ian,

    I would characterize the accretion disk more like a crêpe and not like a pancake.
    My scientific argument is that a crêpe is much closer to the consistency of all the accretion disks I visited recently.

    Also i strongly plead to verify whether the process of ‘being sucked into a death spiral’ is painful.
    My last experience about this happening was extremely joyful.
    I would even tend to say extraordinary mindbugglingly pleasing and enjoyable.

    Last but not least we should stress the point that all the civilisations that would orbit around the star that slowly but with titanic power and ineluctable dies into the greedy blackhole, very likely are doomed. The only way out for them is collective suicide or interstellar space travel

    What do you think ?

  3. 😆
    pradipta you are even better than Ian.

    What if you and Ian join forces and build the ultimate braintrust ?

  4. We can see only light and lighted objects. We can see nothing in the darkness. We are only capable to see the original objects of solar system within the radius of 150 million kilometer from us. Ahead of it everything is mere image into space mirror.
    Visit to know the original truth and wish you to do best for prosperous space research.

  5. super interesting. Am always amazed at the power of the forces at work in the universe. If the universe is in fact designed the designer(s) have a dramatic flair I can appreciate.

  6. Thanks Ian, a very good article . I tracked down the original paper and it seems to be an excellent example of astrophysical modeling presented in sufficient detail and clarity that it might be of interest to senior undergraduate students in physics or in a related discipline. For those interested it is available at arXiv:0707.2476v2 [astro-ph] 22 Jan 2008.

  7. Perfect.
    Thanks Ian, another sparkler.
    Thats what I like about your articles.
    They deliver what I need. Always.

    I can almost hear the dying star mauling.
    Slowly, but with a sound that shakes the entire universe. A very low infra or something sound.

    Wouldn’t this sound even create earthquakes here on earth ?
    I think at least on the side of the earth that faces the black hole.

    Sigh. Thats so beautiful scary.
    And I can understand everything even without a college education.

    Thank you Ian, your fan Bellinda

  8. Yeah Bellinda,

    I can only confirm what you say.
    Ian is my buddy.
    He has the right style to make science hot and spicy.

    During all my high school times I hated mathematics cause it hated me.
    I have been in love with other things. Real life and stuff.
    Ian takes away my shortcomings.

    I understand now immediately all the secrets of the universe, all without algebra and trigonometry.
    And there is even action in the plot, not that boring ages and millions over millions of years and light years. Pure action and cool special effects

    Ian keep it coming. You are the hero of us pedestrians.

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