Illustrations by Liz Zonarich/Harvard Staff

Science & Tech

Strange galactic facts

Sy Boles

Harvard Staff Writer

May 15, 2025

1 min read

Test the limits of your cosmic IQ by taking our quiz based on Harvard astronomy research

There’s nothing quite like looking up at the sky on a dark night and catching a glimpse of the path of light we know as the Milky Way. More than 400 years ago, Galileo viewed the Milky Way through a rudimentary telescope and determined that it was made up of innumerable individual stars. Today we know much more about our own galaxy and countless others, but major questions remain unanswered.

Scientists at the Center for Astrophysics | Harvard & Smithsonian are researching some of our biggest questions about galaxies. We asked CfA researcher and Harvard Ph.D. student Vedant Chandra to help develop this quiz about what we know so far, and what remains to be discovered.

Research from the CfA is supported by the Smithsonian, a federally funded trust.

Step 1 of 10

10%

1. How many galaxies do scientists estimate to be in the universe?

Up to 10 million

1 million – 1 billion

1 billion – 100 billion

100 billion – 1 trillion or more

2. What fraction of a typical galaxy’s mass is made up of ordinary matter like stars and gas?

Less than 5 percent

21 percent

67 percent

100 percent

3. Scientists sometimes group galaxies into several types, some of which were developed by Edwin Hubble back in 1926. Which of the following is NOT a common classification?

Spiral galaxies

Elliptical galaxies

Lenticular galaxies

Blended galaxies

Irregular galaxies

4. Centaurus A, a galaxy about 12 million light-years from Earth, is unusual in what way?

It has lobes emerging from its center, perpendicular to its disk, formed by energetic jets emitted by the supermassive black hole at the center of the galaxy

It’s an elliptical galaxy with spiral arms, a sign that it merged with a spiral galaxy

It is a so-called starburst galaxy, which has recently undergone an unusually intense period of star formation

All of the above

5. On the largest scales, galaxies are evenly separated from one another. True or false?

True

False

6. Which of the following methods is NOT used to measure distances to other galaxies?

Measuring the brightness of stellar explosions called “supernovae”

Measuring the apparent size of galaxies

Measuring the travel time of radio waves to and from the galaxy, also called radar ranging

Measuring the speed at which a galaxy is moving away from us

Measuring random noisy fluctuations in images of galaxies

7. Where can we find the oldest stars formed in the Milky Way, which were born almost 14 billion years ago?

They are no longer alive

At the center of the Milky Way

In the neighborhood of the sun

In the farthest outskirts of the Milky Way

8. The Milky Way steals stars from other galaxies. True or false?

True

False

9. Lenticular galaxies are an intermediate type of galaxy halfway between ellipticals and spirals: They have large stellar disks, but no spiral arms. Which of these lenticular galaxies is not like the others?

NGC 4550

NGC 4866

NGC 5308

NGC 5866

10. The supermassive black hole at the center of our galaxy, Sagittarius A*, is mostly dormant, but it hasn’t always been so. When was the last time our black hole demonstrated significant activity?

The Middle Ages, when early astronomers believed astrological phenomena were omens of death

About 6 million years ago, when the earliest hominids were beginning to walk upright

About 200 million years ago, when all of Earth’s continents were joined in the supercontinent Pangea

About 4.9 billion years ago, before the Earth had formed

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