“Brown dwarf collisions. Want to make a star, but you didn’t accumulate enough mass to get there when the gas cloud that created you first collapsed? There’s a second chance available to you! Brown dwarfs are like very massive gas giants, more than a dozen times as massive as Jupiter, that experience strong enough temperatures (about 1,000,000 K) and pressures at their centers to ignite deuterium fusion, but not hydrogen fusion. They produce their own light, they remain relatively cool, and they aren’t quite true stars. Ranging in mass from about 1% to 7.5% of the Sun’s mass, they are the failed stars of the Universe.
But if you have two in a binary system, or two in disparate systems that collide by chance, all of that can change in a flash.”
Nothing in the Universe exists in total isolation. Planets and stars all have a common origin inside of star clusters; galaxies clump and cluster together and are the homes for the smaller masses in the Universe. In an environment such as this, collisions between objects are all but inevitable. We think of space as being extremely sparse, but gravity is always attractive and the Universe sticks around for a long time. Eventually, collisions will occur between planets, stars, stellar remnants, and black holes.
“4.) There are no neutron stars or black holes within 10 parsecs. And, to be honest, you have to go out way further than 10 parsecs to find either of these! In 2007, scientists discovered the X-ray object 1RXS J141256.0+792204, nicknamed “Calvera,” and identified it as a neutron star. This object is a magnificent 617 light years away, making it the closest neutron star known. To arrive at the closest known black hole, you have to go all the way out to V616 Monocerotis, which is over 3,000 light years away. Of all the 316 star systems identified within 10 parsecs, we can definitively state that there are none of them with black hole or neutron star companions. At least where we are in the galaxy, these objects are rare.”
In the mid-1990s, astronomy was a very different place. We had not yet discovered brown dwarfs; exoplanet science was in its infancy; and we had discovered 191 star systems within 10 parsecs (32.6 light years) of Earth. Of course, low-mass stars have been discovered in great abundance now, exoplanet science has thousands of identified planets, and owing to projects like the RECONS collaboration, we’ve now discovered a total of 316 star systems within 10 parsecs of Earth. This has huge implications for what the Universe is actually made of, which we can learn just by looking in our own backyard. From how common faint stars are to planets, lifetimes, multi-star systems and more, there’s a huge amount of information to be gained, and the RECONS collaboration just put out their latest, most comprehensive results ever.
“All the evidence for dark matter and dark energy seem to be way out there in the cosmos. It seems very suspicious that we don’t see any evidence of it here in our own solar system. No one has ever reported any anomaly in the orbits of the planets. Yet these have all been measured very precisely. If the universe is 95% dark, the effects should be locally measurable.”
You know the deal with dark matter: it makes up 85% of the mass of our Universe, it has gravitational effects but no collisions with normal matter or itself, and it explains a whole slew of cosmological observations. But why, then, if it’s everywhere, including in an enormous, diffuse halo around our Milky Way, doesn’t it affect the motion of our Solar System in an observable way? Surely, when you say that matter is distributed all throughout our galaxy, that will include the Sun’s neighborhood, right? The truth is, it actually does! Dark matter must exist throughout the Solar System, but that doesn’t mean its effects are observable. Contrariwise, you have to do the calculation to know what its density is, and to quantify the effects it would have on the planets. We can actually do this ourselves, and the results we find tell us, under a variety of conditions, exactly what we’d expect. Dark matter should be in our Solar System, and our best observations aren’t yet able to test whether it exists or not!
“When we look at our Universe, where our own galaxy contains some 400 billion stars and there are some two trillion galaxies in the Universe, the realization that there are around ten planets for every star is mind-boggling. But if we look outside of solar systems, there are between 100 and 100,000 planets wandering through space for every single star that we can see. While a small percentage of them were ejected from solar systems of their own, the overwhelming majority have never known the warmth of a star at all. Many are gas giants, but still more are likely to be rocky and icy, with many of them containing all the ingredients needed for life. Perhaps, someday, they’ll get their chance. Until then, they’ll continue to travel, throughout the galaxy and throughout the Universe, vastly outnumbering the dizzying array of lights illuminating the cosmos.”
According to the International Astronomical Union, planets need to have enough mass to pull themselves into hydrostatic equilibrium, they need to orbit a star and not any other object, and they need to clear their orbits in a certain amount of cosmic time. But what do you call an object that would have been a planet, if only it were in orbit around a star, but instead wanders through the heavens alone, unbound to any larger masses? These rogue planets are surprisingly ubiquitous in our galaxy and beyond, and we expect that they’ll far outnumber not only the stars, but even the planets that are found orbiting stars. Where do these rogue worlds come from? A percentage of them are orphans, having been ejected from the solar system that they formed in, but the overwhelming majority ought to have never been part of a star system at all.
Go tell your ex this fact
In a recent post we demonstrated using the Newton’s cannon thought experiment that:
ISS and other satellites are always falling, but they are falling in Orbit
And this applies to planetary bodies too: Earth is always trying to fall into the sun, but it keeps falling in an orbit instead
Well, to answer that question one needs to go back 4.6 Billion years ago and look at the formation of the solar system.
And if you like numerical simulation and are wondering how could a spinning cloud of gas eventually form planets, take a look at the following video and its source paper.
Thanks for asking!
“So why are all the planets in the same plane? Because they form from an asymmetric cloud of gas, which collapses in the shortest direction first; the matter goes “splat” and sticks together; it contracts inwards but winds up spinning around the center, with planets forming from imperfections in that young disk of matter; they all wind up orbiting in the same plane, separated only by a few degrees — at most — from one another.”
When we look out not only at our own solar systems, but at the solar systems we’ve found around other stars, we find they have a remarkable feature in common: their planets all appear to rotate in the same plane. They might be off by a handful of degrees, but as far as we can tell, they all align with one another. This isn’t some mere coincidence, but seems to be a consequence of how solar systems form in the first place. Just as spiral galaxies orbit in the same, single plane, so do solar systems. Remarkably, it seems to be the same process at play: large structures collapse, which they do faster in one direction, and then angular momentum takes over, forming a disk. Over time, imperfections in the disk fragment, causing clumps to form and grow over time. When all is said and done, the survivors are all left in the same, single plane.