What is the paradox of thrift, concept popular among Keynesian economists?

https://www.google.com/amp/s/www.thehindu.com/specials/text-and-context/the-paradox-of-thrift-does-a-rise-in-savings-cause-a-fall-in-investment/article68120811.ece/amp/

What do you understand by quarks and neutron star? How quarks hold the key to the final fate of some stars? Explain.

https://www.thehindu.com/sci-tech/science/massive-neutron-stars-quark-matter-open-problem/article68128512.ece/amp/