Boiled gas giant: What's left behind? + Cosmic Inflation: it perfects Big Bang theory

Cosmic Inflation - the idea that perfects Big Bang Theory

EXCERPT: . . . But the Big Bang does not yet explain it all. Although by the 1970s the Big Bang seemed to outweigh competing ideas about the formation of the cosmos, it left some problems unsolved.

The first was causality. To astronomers’ amazement, they found the CMB’s temperature was uniform everywhere they looked, to a high level of precision. If the universe began as a hot, primeval fireball, why would temperatures everywhere be so uniform? Leaving this enigma unsolved would threaten the Big Bang idea.

The second was the flatness problem. The cosmological number Omega (Ω) describes both the universe’s shape and fate. Astronomers found Omega’s value equals 1, which seemed highly coincidental. A number less than 1 would mean space is open and will continue to expand forever; greater than 1 would mean a closed universe and an eventual “Big Crunch”, with the cosmos falling back on itself.

The third was the magnetic monopole problem. The cosmos is filled with electric monopoles, particles like electrons and protons. But astronomers have not observed any magnetic monopoles. The lack of these particles bothered particle physicists.

In 1981, to solve these problems, scientists presented a new idea that expanded the Big Bang theory and added weight to it. Alan Guth [...] wrote a paper that described the “inflationary” model of cosmology, developed with his colleagues Andrei Linde, Paul Steinhardt, and Andy Albrecht. Inflation proposes a short period of expansion - 10^-34 second - in the early universe. As astrophysicist Mario Livio says, “All inflation theories … grab a speck of space and blow it up by a factor of 10⁵⁰.” Inflation resolves some questions surrounding the Big Bang... (MORE - details)

What’s Left Behind When You Boil A Gas Giant?

EXCERPTS: . . . For generations, we assumed that if there were planets around stars other than the Sun, they might follow the same generic pattern that we observe here: inner, rocky planets, outer, gas giant planets, with asteroids in between and icy worlds beyond them all. With the first few thousand planets under our belt, we now know that our Solar System isn’t typical at all, and that planets come in a wide variety of masses, radii, and orbital distances. Moreover, they fall into not two, but three general categories: rocky worlds, small gas giants with hydrogen/helium envelopes, and massive gas giants that exhibit self-compression.

[...] But deep inside the giant worlds of our Solar System, beneath the various layers of volatile gases, lies a massive core rich in heavy elements. Each one contains a rocky core that’s significantly more massive than any of the “rocky” planets in our Solar System, with the gravitational force sufficient - at their great distances from the Sun - to hold onto the light elements in their outer atmospheres. But not every gas giant is so lucky; some of them should be too close to their parent stars, where their volatile gas atmospheres are boiled away. Here’s what’s left behind.

[...] There appears to be a threshold: once the mass of your core gets to about 10 Earth masses or more, it will start to accrue large amounts of hydrogen and helium very quickly, leading to the possibility of it growing into a gas giant with self-compression. Below that threshold, and you might still make it to a hydrogen/helium envelope, but you’re more likely to be Neptune-sized than Jupiter-sized. In our own Solar System, the cores of Neptune and Uranus failed to meet this threshold, while Jupiter likely passed it quite early. Saturn is a sort of in-between case, as its core has an uncertain mass that may fall either below or above that threshold, but is close in either case.

But in other solar systems, there are a few outliers that don’t follow these trends exactly. In particular, there are quite a few exoplanets known that are between 1 and 2 Earth radii, but can be many times the mass of Earth: up to 20 Earth masses or so! That’s like having a planet equal to the mass of Neptune or Uranus, but contained in a volume that’s only a few times larger than Earth’s. In other words, these planets have to have densities comparable to or even greater than our own planet’s, meaning they must be composed almost entire of rocky/metallic material.

Planets such as this, interestingly enough, are almost exclusively found very close to their parent star. [...] The only reasonable way for this to form is if this exoplanet is the stripped core of a gas giant: one that has been too close to its parent star for too long to hang onto its hydrogen and helium envelope. ... These worlds might represent an uncommon fourth class of planet, but further observations are necessary to know for certain... (MORE - details)

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