Space & astronomy · the experiment
Weigh the invisible partner
Every 4.2 hours, a stripped star circles something that does not shine. Measure its swing, then weigh that partner.
1 · Read the lines
Beginner
DGL-3's partner gives off no light. What gave its presence away?
Move the orbit forward and stop when the star is moving away from us fastest.
2 · Weigh the partner
Take the star at 3.4 solar masses and the orbit seen edge-on: all of its speed is then along our line of sight.
Intermediate
With the star at 3.4 M☉ and the orbit seen edge-on, you get about 1.07 M☉, below the 1.4 M☉ a white dwarf cannot exceed. What do you conclude?
Set the partner's mass until the model curve matches the measurement.
3 · 1.07 or 1.38?
Expert
For an orbit seen edge-on, the article gives a typical minimum partner of 1.38 ± 0.25 M☉. Where does the gap with your result, around 1.07 M☉, come from?
4 · Tilt the orbit
The star stays at 3.4 M☉. The partner goes to 1.4 M☉, the white-dwarf ceiling: seen edge-on, the star would swing too fast.
Expert
Edge-on, 1.07 M☉; tilted, 1.4 M☉: the velocity curve is the same. Which measurement in the article can tell these two cases apart?
Tilt the orbit until you recover the measured speed.
Partner weighed
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