<Dl> <Dd> <Table> <Tr> <Td> </Td> <Td> + </Td> <Td> </Td> <Td> → </Td> <Td> 2 γ </Td> <Td> + </Td> <Td> 6987163422001674000 ♠ 1.02 MeV </Td> </Tr> </Table> </Dd> </Dl> <Dd> <Table> <Tr> <Td> </Td> <Td> + </Td> <Td> </Td> <Td> → </Td> <Td> 2 γ </Td> <Td> + </Td> <Td> 6987163422001674000 ♠ 1.02 MeV </Td> </Tr> </Table> </Dd> <Table> <Tr> <Td> </Td> <Td> + </Td> <Td> </Td> <Td> → </Td> <Td> 2 γ </Td> <Td> + </Td> <Td> 6987163422001674000 ♠ 1.02 MeV </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> + </Td> <Td> </Td> <Td> → </Td> <Td> 2 γ </Td> <Td> + </Td> <Td> 6987163422001674000 ♠ 1.02 MeV </Td> </Tr>

What is the threshold temperature for the fusion of hydrogen to helium to occur