What Would Happen if a Habitable Planet was Discovered?

Question: If an earth-like planet was discovered by a large US observatory that virtually guaranteed the capability of supporting life, would it be announced to the public straight away? Or would/could the government intervene and likely suppress news of the discovery for some reason? How would other nations observatories and governments likely react if they made such a find?  – Bruce

Answer: I cannot think of any reason why such a discovery would be kept secret.  Such a discovery would likely spur an increase in measurements of this newly-discovered planet, which would likely encourage governments to increase their investments in the science associated with the study of this planet.

Jeff Mangum

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The Density of Matter in a Black Hole

Question: A 10 solar mass object would have 10 solar masses enclosed in a radius of 30 km.   The density of a spherical object scales as M/R3.  Relative to the 10 solar mass black hole, how many times denser would a black hole the mass of the Earth be?  How many times less dense would a black hole of 1 million solar masses be?  – Paul

Answer: As my colleague Cole Miller points out in his description of the properties of black holes and neutron stars, unlike ordinary things (e.g., rocks), which have a size roughly proportional to the cube root of their mass, black holes have radii proportional to their mass.  Taking the event horizon of a black hole as the definition of its outer boundary, the event horizon of a nonrotating black hole the mass of our Sun would have a radius of about 3 kilometers.  This implies that the more massive the black hole is the denser it is, meaning that larger black holes are not very dense.  For example, a one-billion solar mass black hole, which is the type of black hole that is thought to exist at the center of some galaxies (like ours), has an average density just twenty times the density of air.

Jeff Mangum

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A Question About a Career in Astronomy

Question: How can I get involved in a career uncovering the “unexplained” of the universe? I am interested in that particular part of astronomy, but I am not sure if it is too specific, or something that I cannot easily obtain. To put it into perspective, I am interested in astronomy AND astrology (myths, greek mythology, etc). (I bet you are laughing!) I am a 25 year old, and looking to go back to school once and for all. What advice do you have for me?  – Sam

Answer: You should look at the information on my Careers in Astronomy page for information, including questions and answers from people like yourself who are interested in a career in astronomy science in general.  Note that studying the sciences does not exclude the study of those aspects in our culture that sometimes conflict with the results that come from scientific investigation.

Jeff Mangum

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Questions About Cosmology and Catching Near Earth Objects

Question #1: Hello there! Sorry for the previous thing I had sent, it was merely a comment. I am a 16 year old high school student who is interested in the study of the stars and our universe itself.  And I also have a theory to which, I would highly appreciate if you took the time to read it. You know the candle light variable used to measure the distance of us from a certain star? With that being said, there is also the situation of our universe expanding farther away, and the theory of how it will stop and come back to it’s center of where it began, which is where the Big Bang theory comes from. Now, I know this sounds a bit crazy. But hear me out. Since our entire universe is made up of dark matter, also a compound in the creation of our universe with the gas and dust that creates stars, the universe coming back together, crunching into one could cause another Big Bang. In which case, would be the same illusion as a star pulsating it’s light. What if we are only specs of particles and molecules created to make one big star? What if our whole universe if just one star as we know it, and there are billions upon billions of stars, that make up universes?  – Rachel

Answer #1: All theories, whether they be to explain the evolution of the universe or the properties of a star, require measurements to support them.  What measurements support your theory?  This is the key to any scientific investigation that involves theory which must ultimately be supported by observations.


Question #2: Also, I’d like to mention that I have an idea for a device that could be placed a certain distance away from Earth, enough not to mess with the gravitational pull, and take the near earth objects that could be potentially dangerous by coming to close and crashing in Earth. What if they made a device to take these potentially dangerous items and drag them away from Earths surface, and had a inside that could destroy the items inside? This device could also be used for meteorites, to pull them away from the Earth’s gravitational pull. Also, with delittering the area, you could catch more light in telescopes and would be allowed to possibly see things even farther than we ever have. Please message me back, telling me what you think!

Answer #2: How would this device collect meteoroids and potentially dangerous asteroids?  Note that the sheer number of meteoroids and asteroids that this device would need to collect would make any “scooping” device not practical.


Jeff Mangum

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In What Direction Does the Outflow from a Quasar Go?

Question: Thank you for answering! Is the supposed spinning the reason all the body’s caught in the pull stay in a synchronized belt around it? If so, where does a quasar emit? “North and south?” Or anywhere it pleases? I know very little known, but these questions are the reason I can’t sleep at night.  – Nathan

Answer: Quasars emit their outflows which are suggested to coincide with the rotation axis of an embedded black hole.  This direction is preferred as it represents the direction where the angular momentum is lowest, thus allowing the outflow material to propagate away from the black hole.

Jeff Mangum

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Does the Sun’s Rotation Speed Dictate the Orbital Speed of the Planets?

Question: Are the planets orbiting the sun at the same speed as the sun revolves on its axis? Or are some planets moving slower or faster than the sun spins, of course the position in the solar system dictates how long it takes to complete one full orbit, but say they were all in the same position close to the sun are they moving at the same speed as the sun spins? When the solar system formed surely the sun dictated the speed at which the dust cloud revolved, so unless objects got bumped to move faster or slower they should all be revolving roughly the same yes??  – Sammy

Answer: The Sun takes about 26 days (at its equator) to 34 days (at its poles) to rotate on its axis at its equator, which is much faster than all of the planets orbit about the Sun.  In fact, the orbits of the planets are dictated (mostly) by the Sun’s gravity and their distance from the Sun.  Also, the speed at which the dust cloud from which the Sun and planets formed was determined by the mass and angular momentum of the cloud itself, as it was much more massive than the Sun and planets.

Jeff Mangum


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Where is the Center of the Big Bang?

Question: My understanding is that the COBE experiments back in the late 80s/early 90s were successful in detecting what we generally believe to be the CMB leftover from the big bang.

In reading about the experiment I haven’t had much luck finding an answer about if COBE (or some other experiment) has been able to estimate a vector, or general location, for the big bang itself. Do we have any data that allows us to extrapolate where, geographically in the universe, the big bang might have been? Would this be a safe/fair location to consider the “center of the universe” if it were known?  – Tim

Answer: In fact, there is no “center” to the Big Bang.  The Big Bang was not an explosion which radiated from a point but rather an expansion of all points from all other points in the Universe.  One of the best pictorial descriptions of this fact can be found on Ed Wright’s Big Bang “nocenter” page.  This is part of the “cosmological principle, which states that all positions in the universe are equivalent, and that the universe is homogeneous.

Jeff Mangum

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Can a Neutron Star Become a Black Hole?

Question: Can you help with this new question could a man made neutron star be made to then collapse it into a black hole, but I am not sure if it is answerable.  A neutron generator can generate to 108 neutrons per second.  A 1 microampere ion beam accelerated at 200 kV to a titanium-tritium target can generate up to 108 neutrons per second. The neutron yield is mostly determined by the accelerating voltage and the ion current level.  If you were going to attempt to create a man made neutron star using a neutron generator in space, because this is the only place where you could do this experiment.  First using the neutron generator which can make 108 neutrons per second, you would start by putting all the neutrons into one place.  As you generate, and put all the neutrons into one place you would probably have a microscopic sphere of neutron matter after a while.  So here is the problem, I do not know the exact point in spherical mass where neutrons become stable in a neutron star, because its the pressure from gravity that is compacting them, and stopping them from decaying back to protons.  If you knew the exact point in spherical mass where neutrons become stable with gravity, you could calculate the number of neutron generators you would need, with the time that the neutrons would decay back into protons.  The other thing I do not know is does the exact point in spherical mass in a neutron star where neutrons are stable,  would that exact point in a spherical mass of neutrons have the same strength gravity as a medium sized star to crush the neutrons into place, and keep the neutrons stable, as you were putting them together with the neutron generator.  Making a sphere the size of a mile may not be enough because you would have to compact the neutrons together closely in the same way a medium sized star does to keep the neutrons stable from decaying.  So does a mile, or more of a sphere of non-compacted neutrons be enough to create a gravitational field as strong as a medium sized star, or does the sphere of neutrons need to be compacted together more to create stronger gravity to hold the neutrons into place.  So to put it as simple as possible is putting neutrons together in a sphere a mile or more in spherical mass going to create enough gravity to compact the neutrons into place to keep the neutrons stable from decaying into protons.  Getting more material to complete this man neutron star to collapse it into a black hole would not really be a problem if you parked it next to a giant star, because the gravity would draw in the material from the giant star and add it to its own mass to make it larger, and I read somewhere the neutron star would not burn so close to a giants star, to absorb its material, and add it to its own mass.  Can you help with any of the questions.  – Nicholas

Answer: I think that your question is whether a neutron star can become a black hole.  Neutron stars are thought to have masses between the Chandreskhar limit of 1.39 solar masses to about 3 solar masses.  If a neutron star gathers more mass and gets to the point where its mass reaches about 10 solar masses, its mass will overcome the neutron degeneracy pressure that supports it against gravity and collapse to become a neutron star.

Jeff Mangum

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When Does the Earth’s Prime Meridian Line Up With the Celestial Meridian?

Question: On what date and time to the nearest second (in the past) has earths prime meridian directly lined up and faced the
“celestial meridian” and I am talking about using the “equatorial coordinate system”

Definition for “Celestial Meridian” which I am using from Dictionary.com below:
“In the equatorial coordinate system, a great circle on the celestial sphere passing through the celestial poles and the vernal equinox. It represents the zero point for the horizontal coordinate in this system, having a right ascension of 0 hours.”

I might have thought it was vernal equinox but that happens once every year but the earth doesnt rotate exactly 360 degrees per year so the prime meridian on earth would not always line up. So thats not my answer so I cant just look up Vernal equinox dates on the web.
Its might happen every 4 vernal equinox but not sure. That still would not give me a date which I am looking for.

Prefer UT time or Julian date but anything would help.
Does the date time I am looking for even have a unique name for it?

– Steve


Answer: The Earth’s “prime meridian” is the great circle which passes through the Earth’s poles and represents the start of the longitude coordinate system, or zero-degrees longitude.  Comparing that to the definition you have given above for the celestial meridian, I would say that these two meridians line up once each day.  The exact time in a day that the prime meridian aligns with the celestial meridian is determined by the difference between a solar and sidereal day, or about 4 minutes.

Jeff Mangum

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How Do Galaxies Stay Intact?

Question: Do black holes spin? What makes galaxies stay semi organised while precessing around it? I don’t know how else to word that. Physics is hard.  –  Nathan

Answer: Yes, it is believed that black holes do spin.  The stars in galaxies stay organized over long periods of time while the galaxy rotates due to the mutual gravitational attraction of the stars, gas, and dust in galaxies.  That gravitational force balances any forces that might pull a galaxy apart, making the galaxy maintain a stable configuration over many millions of years.

Jeff Mangum


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