1)astronomers think the most galaxies are centered by, 2)which exerts that binds the galaxy together

1
a. black hole
b. nebula
c. large planet
d. massive star

2
a. gravitational pull
b. centripetal force
c. magnetic pull
d. centrifugal force

1. 1black hole, 2gravitational

2.Black holes trap all light.

3.the center of the Milky Way

4.Its mass is greater than 20 times the mass of the sun, It is dying

5.interactions with light

6.A massive star depletes its nuclear fuel; gravity overpowers the star; supernova occurs; core of star collapses.

7. 1gravity, 2an explosion

8.These galaxies include irregular, spiral, and elliptical types.

Explanation:

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ecotourism pay for conservation efforts.

1. b.

2. d.

3. a.

5. d.

6. c.

these are the only ones that i know, i hope this , and good luck.