Question 1: The presence of young stars
Question 2: pulls matter together or causes fusion reactions
Question 3: central supermassive black hole, gravitational force
Question 4: These galaxies include irregular, spiral, and elliptical types.
Question 5: A massive star depletes its nuclear fuel; gravity overpowers the star; supernova occurs; core of star collapses.
Question 6: the center of the Milky Way
Question 7: Black holes trap all light.
Question 8: Its mass is greater than 20 times the mass of the sun and It is dying.