Erwin Schrödinger's famous book,
What Is Life? begins with a simple question:
"Why are the atoms so small?"It subsequently turns this question around: "Why must our bodies be so large compared with the atom?"
The point is that a brain (a 'thinking' system) must consist of an enormous number of atoms. Magnitude is only part of the answer; the other essential quality is that of organization.
There was a recent article on HN: "Is the emergence of life an expected phase transition in the evolving universe?" (https://news.ycombinator.com/item?id=39103419)
Stars are chemically relatively simple (for example: Introduction to Astrochemistry: Chemical Evolution from Interstellar Clouds to Star and Planet Formation by Satoshi Yamamoto).
It takes a lot of evolution to arrive at even a simple cell. Early Evolution: From the appearance of the first cell to the first modern organisms by Martino Rizzotti, begins with this sentence: "It is now accepted that the first cells derived from simpler 'objects', and that their descendants became more and more complicated and ordered until their evolutionary transformation into modern cells..."
Brain Evolution by Design: From Neural Origin to Cognitive Architecture edited by Shuichi Shigeno, Yasunori Murakami, and Tadashi Nomura discusses how brains have been shaped by simple evolutionary processes.
Computation in Living Cells: Gene Assembly in Ciliates by Andrzej Ehrenfeucht Tero Harju, Ion Petre David M. Prescott, and Grzegorz Rozenberg, goes further to discuss natural computing, which requires (as per What Is Life?) a certain level of biology.
The key point in these studies is that evolution seems to imply increasing complexity.
John W Campbell summarized it nicely in an editorial in Astounding Science Fiction, December 1955, Necessary Isn't Sufficient:
"A vast mass of gas in interstellar space is perfectly stable as it drifts idly around. Organize it a little, and a chain-reaction of increasing complexities is initiated; organization breeds organization, seemingly. The gas, once it is organized above a certain critical level, begins to fall together by mutual gravitation. If the organization is large enough and the necessary intensity of organization is achieved, the deuterium-deuterium reaction begins, and the gas mass is no longer stable. A star begins to glow.
"The gas-and-dust mass has, meanwhile, been undergoing sub-organization that produces planets circling the star. What happens on the planets, we certainly are not yet competent to define - but we know with absolute certainty that, in some instances, a higher-order organizational complexity called Life arises. And that this organization breeds further and higher-order organization."
Stars lack this essential complexity. So, in my opinion, it's silly to suggest that they may be 'conscious'.