Measurements from Distant Galaxies Indicate That Supernovae Should Occur at a Rate

question 66

Multiple Choice

Measurements from distant galaxies indicate that supernovae should occur at a rate of 5 per century in a spiral galaxy such as the Milky Way, but only 3 have been recorded in this Galaxy in the past 1000 years. Explain.

• A) Most supernovae produce X-rays and radio waves, not visible light, and were hence invisible to earlier observers.
• B) The majority of supernovae must have occurred in the plane of the Milky Way and hence were hidden from Earth by the dense gas and dust in the Milky Way plane.
• C) The Milky Way Galaxy is somehow different, with much lower numbers of very massive stars in general, so many fewer stars have undergone supernova explosions.
• D) Observers were not watching the sky carefully enough, particularly through the Dark Ages and over the past few centuries.

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Definitions:

End-Systolic Volume

The volume of blood left in the ventricle after contraction (systole) and before it begins to fill again.

Cardiac Output

The volume of blood the heart pumps through the circulatory system in one minute, a critical measure of heart function and efficiency.

Stroke Volume

The amount of blood the heart ejects with each beat, a key component in determining cardiac output.

Venous Return

Volume of blood returning to the heart.