What Happens to a Black Hole That Radiates to “Nothing”?

Question: Just to clarify, Hawking’s radiations takes place simultaneously to the black hole growing? and, then becomes dominant once the black hole stops growing?  Further, having depleted with a final outburst/explosion leaving behind ” nothing ” – to what level is this “nothingness” defined? No mass,no energy,no waves, no “quantum fluctuations”?..no dark matter, no dark energy? It seems to be that it is becoming increasingly difficult to define ” nothing “?!  – Simon

Answer: As you have said, “Hawking Radiation” is the theoretical process by which black holes that spin lose energy (and, therefore, mass).  For black holes that lose more mass than they gain (i.e. those that do not collect a lot of mass due to accretion), in theory a black hole can lose all of its mass and “vanish”.  This means that all matter associated with the black hole has been emitted as energy.

Jeff Mangum

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Do Black Holes Move Through Spacetime?

Question: Does a black hole move through spacetime or does it draw spacetime to “it” giving the illusion its moving?  – Nigel

Answer: Black holes move through spacetime just like any other object in the universe.  It is true, though, that black holes “warp” spacetime more than other objects due to their extremely intense gravitational field.

Jeff Mangum

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How Can Jets of Matter Escape a Black Hole?

Question: I don’t understand this:
I read somewhere (and this isnt a quote but its close enough) that

….the gravitational pull of a black hole is so great that nothing can escape from it – not even light ( thats what makes them black).

I also read that its the general scientific concensus that nothing can go faster than light ( or else some law is getting broken or something like that)…..so doesn’t this mean that the stuff in the jets escaping out of black holes is going faster than light can go ,cos light cant get out?  – Nigel

 

Answer: The matter that we observe as jets emanating from a black hole are not actually coming from the black hole itself.  The jets are composed of matter which is escaping from the accretion disk which surrounds the black hole.  Although the mechanism by which the jets are produced is not completely understood, the process likely involves the acceleration of matter near the poles of the black hole and an interaction with the tangled magnetic field in the region near the poles of the accretion disk.  The material in the jets is measured to be travelling at less than the speed of light.

 

Jeff Mangum

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A Black Hole That Comes Back to Life?

Question: My partner was driving  home yesterday night ( 29 june 2015) listening  to the radio, they were talking about a black hole that they realised had came back to life again.  Would you know specific black hole they talking about?  Or what constellation its near to.  Like i said my partner was hearing  it on the radio on the 29 june 2015.  – Pete

Answer: I suspect that the story you heard was about V404 Cygni, which is a black hole and star system in our galaxy, in the direction of the constellation Cygnus, which has recently “flared”, or produced an outburst of energy at xray wavelengths.  Although the specific mechanism by which black holes flare is not entirely understood, it likely has something to do with the amount of matter being fed to the black hole (by, in this case, the nearby star that is gravitationally coupled to the black hole).

 

Jeff Mangum

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What Lies Beyond the Known Universe?

Question: Do dimensions really exists? [Also,] are the black holes really or possibly portals leading to different dimensions (like a whole new universe or a totally different universe)?  [Also,] right now I read in the blog about like the diameter of universe being 96 billion light years (in other sense the universe being confined within these 96 billion light years diameter) so what lies beyond that diameter?  – Pravesh

Answer: One can speculate or theorize as to what exists beyond that which we can measure, but that is, strictly speaking, not science.  What scientists do is make observations of the universe and apply the laws of physics to those observations to interpret what they observe.  As there are no actual observations which can tell us what lies beyond a black hole or the edge of the universe, we can only speculate or theorize as to what might lie beyond what we observe.  To my knowledge there are no theoretical predictions which are based on physics which predict what lies beyond black holes or the edge of the universe, which leaves us only speculation, which is not science.  So, a scientist would answer that there is no information to tell us what lies beyond a black hole or the edge of the universe.

Jeff Mangum

 

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How To Make Images With a Radio Telescope

Question: I just started radio telescope observation, and wanted to know how to use a computer to capture actual images or similar with a radio telescope. I am just using an old TV dish with a satellite receiver and LNB, but I still hope I can use it to capture images. How do I plug it in the the computer and use the computer to capture images from the telescope?  – John

Answer: Radio telescopes are just like optical telescopes in that the parts of these telescopes that produce images are actually the detectors that are placed at the focal point.  Optical telescopes use array detectors, such as Charge Coupled Devices (CCDs).  Radio telescopes can also use array detectors to produce images, but these array detector systems are often much more complicated and difficult to make.  The most straightforward way to make a radio image with your satellite antenna system, then, is to use an array detector, which I believe would be very difficult to find.  Alternatively, one can make an image by pointing an antenna to an array of nearby positions on the sky then creating a contour map of the measured signal strength.  This is a rather slow process, though, that only produces an image much later, after you have gathered all of your individual pointing measurements.  Remember, though, that you can do quite a few interesting measurements with your satellite antenna and receiver system.  You might take a look at the web site of the Society of Amateur Radio Astronomers (SARA) for some ideas for measurements that you might try.

Jeff Mangum

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Where Can One Acquire Large Amateur Radio Antennas?

Question: I am an amateur radio astronomer, and am wondering how to proceed from just a small TV dish to a larger dish. Where can I purchase/acquire second hand a larger (6 or more feet in diameter) dish for more detailed images?  – Lars

Answer: I think that a good place to look for information on amateur radio astronomy equipment, including antennas, would be the Society of Amateur Radio Astronomers (SARA).  There is lots of information on the SARA web page that should point you toward a source for larger antennas that can be use for radio astronomy.

Jeff Mangum

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Does the Sun’s Rotational Axis Precess?

Question: The earth has the north celestial pole position today near Polaris and has a 25000 year cycle circle.  What is the same for the SUN’s north celestial pole and wobble?  – David

Answer: The precession of the Earth’s rotational axis comes about due to tidal torques caused mostly by the differential pull on the Earth by the Moon and the Sun.  These tidal torques cause the Earth to become less than spherical (oblate).  The Sun, on the other hand, is very nearly spherical, and its rotation axis is very nearly aligned with that of Jupiter’s (tilt with respect to Jupiter is about 6 degrees).  The Sun also has a relatively small rotation rate of about one revolution every 25.5 days.  All of these factors conspire to produce a very small precession rate for the rotation axis of the Sun.

Jeff Mangum

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Question About Different Research Fields in Astronomy

Question: Hello. I’m a Junior in High school and a sophomore in College. I just recently became interested in the field of astronomy, but I’m having a hard time understanding the different types of astronomy fields there are. I would enjoy to go into the field of planetary or radio astronomy, but was wondering where i could go to understand each of these fields a little better. Also, do you have any suggests for universities that have great astronomy programs?  – Sandra

Answer: Great to hear of your interest in studying astronomy.  Like specialization of research in other scientific fields, planetary and radio astronomy are specializations associated with the study of particular objects and/or using specific wavelengths for study.  Planetary astronomy involves the study of objects in our solar system, and can be defined to include the study of planetary systems outside our solar system (the so-called “extrasolar planets”).  Radio astronomy, on the other hand, involves the use of radio frequency measurements to study a wide range of astronomical objects.  Radio wavelengths span the range from wavelengths of several meters or more to wavelengths as short as a few hundred microns (sometimes referred to as “submillimeter astronomy”).  Every object that is studied using other wavelengths, such as optical wavelengths, can also be studied at radio wavelengths.  Regarding your question about universities with good astronomy programs, I can say that there are many!  The best way to find a graduate program in astronomy is to look at the web pages for any astronomy program that you might be interested in and look at the research that the faculty in that department are working on.  If you find a researcher whose work you find interesting, contact them for more information.  Most astronomers are more than happy to discuss their work with students.

Jeff Mangum

 

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Does the Moon Bend Radio Waves?

Question: Regarding radio astronomy, are there any “edge effects” to the moon, meaning can or does the moon bend or diffract radio waves emanating from behind it?  Is it possible it bends it enough to create a focal point on the earth?  What frequencies might be the most feasible for studying this?  – David

Answer: Yes.  Think of radio wavelength “light” as having the same properties as optical light, but having a longer wavelength.  In fact, even though the original observations, made in 1919, of the general relativistic prediction that light would bend as it passes around the edge of the Moon were made at optical wavelengths, those early measurements were somewhat inaccurate.  The uncertainty of these first and subsequent optical measurements remained quite large until the 1960s, when measurements at radio wavelengths were made which confirmed Einstein’s theory of general relativity.  These observations are generally done at centimeter wavelengths, which are a good choice for the availability of high-sensitivity facilities, such as the Very Large Array.

Jeff Mangum

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