请问为什么某些进程kill不掉

UPO-JZSBMBP:~ zhaoliang$ ps aux | grep osu.ppy | grep -v grep
zhaoliang 45825 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45793 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45791 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45784 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45777 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45765 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
UPO-JZSBMBP:~ zhaoliang$ echo $( ps aux | grep osu.ppy | grep -v grep | awk '{print $2}' | tr '\n' ' ')
45825 45793 45791 45784 45777 45765
UPO-JZSBMBP:~ zhaoliang$ sudo kill -9 $( ps aux | grep osu.ppy | grep -v grep | awk '{print $2}' | tr '\n' ' ')
UPO-JZSBMBP:~ zhaoliang$ ps aux | grep osu.ppy | grep -v grep
zhaoliang 45825 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45793 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45791 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45784 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45777 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
zhaoliang 45765 0.0 0.0 2423412 16 ?? S 19 915 0:00.14 /usr/bin/open http://osu.ppy.sh/b/211502&ch=overall
UPO-JZSBMBP:~ zhaoliang$